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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2018	Feb. 21, 2019	Jun. 29, 2018
Document and Entity Information
Entity Registrant Name	MADRIGAL PHARMACEUTICALS, INC.
Entity Central Index Key	0001157601
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2018
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 2,320,321,944.81
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		15,417,064

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 57,379	$ 148,627
Marketable securities	426,339	42,900
Prepaid expenses and other current assets	1,483	485
Total current assets	485,201	192,012
Property and equipment, net	227	301
Total assets	485,428	192,313
Current liabilities:
Accounts payable	2,487	1,929
Accrued expenses	5,957	8,125
Total current liabilities	8,444	10,054
Total liabilities	8,444	10,054
Stockholders' equity:
Preferred stock, par value $0.0001 per share authorized: 5,000,000 shares at December 31, 2018 and December 31, 2017; 1,969,797 shares issued and outstanding at December 31, 2018 and December 31, 2017
Common stock, par value $0.0001 per share authorized: 200,000,000 at December 31, 2018 and December 31, 2017; 15,409,023 and 14,227,634 shares issued and outstanding at December 31, 2018 and December 31, 2017, respectively	2	1
Additional paid-in-capital	616,573	288,750
Accumulated other comprehensive loss	(319)	(31)
Accumulated deficit	(139,272)	(106,461)
Total stockholders' equity	476,984	182,259
Total liabilities and stockholders' equity	$ 485,428	$ 192,313

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating expenses:
Research and development	$ 25,389	$ 24,390	$ 15,933
General and administrative	15,293	7,672	9,290
Total operating expenses	40,682	32,062	25,223
Loss from operations	(40,682)	(32,062)	(25,223)
Interest expense			(1,213)
Interest income	7,671	558	48
Other income	200	350
Net loss	$ (32,811)	$ (31,154)	$ (26,388)
Net loss per common share:
Basic and diluted net loss per common share (in dollars per share)	$ (2.22)	$ (2.54)	$ (5.07)
Basic and diluted weighted average number of common shares outstanding	14,796,712	12,244,939	5,204,644

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Preferred Stock	Common stock	Additional paid-in Capital	Accumulated other comprehensive income (loss)	Accumulated deficit	Total
Balance at Dec. 31, 2015			$ 6		$ (48,919)	$ (48,913)
Balance (in shares) at Dec. 31, 2015		176,158
Increase (Decrease) in Stockholders' Equity
Related party debt restructuring			11,224			11,224
Conversion of convertible notes and related accrued interest to common stock		$ 1	47,592			47,593
Conversion of convertible notes and related accrued interest to common stock (in shares)		7,087,186
Retirement of restricted stock (in shares)		(9,689)
Acquisition of Synta			38,236			38,236
Acquisition of Synta (in shares)		4,029,138
Issuance of shares to financial advisors in connection with Merger			750			750
Issuance of shares to financial advisors in connection with Merger (in shares)		79,101
Issuance of restricted common shares (in shares)		208,255
Issuance of common shares in equity offering, excluding to related parties, net of transaction costs			5,954			5,954
Issuance of common shares in equity offering, excluding to related parties, net of transaction costs (in shares)		381,717
Compensation expense related to stock options for services			7,929			7,929
Unrealized loss on available-for-sale securities				$ 25		25
Net loss					(26,388)	(26,388)
Balance at Dec. 31, 2016		$ 1	111,691	25	(75,307)	36,410
Balance (in shares) at Dec. 31, 2016		11,951,866
Increase (Decrease) in Stockholders' Equity
Issuance of common and preferred shares in equity offerings, net of transaction costs			173,805			173,805
Issuance of common and preferred shares in equity offerings, net of transaction costs (in shares)	1,969,797	2,275,768
Compensation expense related to stock options for services			3,254			3,254
Unrealized loss on available-for-sale securities				(56)		(56)
Net loss					(31,154)	(31,154)
Balance at Dec. 31, 2017		$ 1	288,750	(31)	(106,461)	$ 182,259
Balance (in shares) at Dec. 31, 2017	1,969,797	14,227,634				14,227,634
Increase (Decrease) in Stockholders' Equity
Issuance of common shares in equity offering, excluding to related parties, net of transaction costs		$ 1	311,824			$ 311,825
Issuance of common shares in equity offering, excluding to related parties, net of transaction costs (in shares)		1,079,580
Sale of common shares to related parties and exercise of common stock options, net of transaction cost			2,510			2,510
Sale of common shares to related parties and exercise of common stock options, net of transaction cost ( in shares)		101,809
Compensation expense related to stock options for services			13,489			13,489
Unrealized loss on available-for-sale securities				(288)		(288)
Net loss					(32,811)	(32,811)
Balance at Dec. 31, 2018		$ 2	$ 616,573	$ (319)	$ (139,272)	$ 476,984
Balance (in shares) at Dec. 31, 2018	1,969,797	15,409,023				15,409,023

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (32,811)	$ (31,154)	$ (26,388)
Adjustments to reconcile net loss to net cash used in operating activities:
PIK interest expense on convertible promissory notes payable - related parties			1,207
Stock-based compensation expense	13,489	3,254	7,929
Other share based compensation			750
Depreciation and amortization expense	96	77
Changes in operating assets and liabilities:
Accounts receivable - related parties			7
Prepaid expenses and other current assets	(998)	502	1,290
Accounts payable	558	917	(128)
Accrued expense	(2,168)	4,087	(2,281)
Accrued interest, net of interest received on maturity of investments	(3,673)
Accrued interest - related party			6
Net cash used in operating activities	(25,507)	(22,317)	(17,608)
Cash flows from investing activities:
Cash received from merger transaction			5,849
Purchases of marketable securities	(614,358)	(70,211)	(10,697)
Sales and maturities of marketable securities	234,304	48,330	26,063
Purchases of property and equipment, net of disposals	(22)	(125)	(3)
Net proceeds from the sale of property, equipment and other assets			698
Release of restricted cash			83
Net cash provided by (used in) investing activities	(380,076)	(22,006)	21,993
Cash flows from financing activities:
Proceeds from issuances of stock, excluding related parties, net of transaction costs	311,825	173,805	5,954
Proceeds from the sale of related party stock and exercise of common stock options, net of transaction costs	2,510
Proceeds from convertible notes - related parties			8,500
Net cash provided by financing activities	314,335	173,805	14,454
Net increase (decrease) in cash and cash equivalents	(91,248)	129,482	18,839
Cash and cash equivalents at beginning of period	148,627	19,145	306
Cash and cash equivalents at end of period	$ 57,379	148,627	19,145
Supplemental disclosure of cash flow information:
Exchange of related party advances payable for convertible notes			500
Related party debt restructuring			$ 13,680
Purchases of property and equipment in accounts payable at period end		$ 250

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Principle of Consolidation

The consolidated financial statements include the financial statements of the Company and its wholly owned subsidiaries. All significant intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect certain reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting periods. The Company bases its estimates on historical experience and various other assumptions that management believes to be reasonable under the circumstances. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.

Cash and Cash Equivalents

The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents. The Company maintains its cash in bank accounts, the balance of which, at times, exceeds Federal Deposit Insurance Corporation insured limits.

The primary objective of the Company’s investment activities is to preserve its capital for the purpose of funding operations and the Company does not enter into investments for trading or speculative purposes. The Company’s cash is deposited in highly rated financial institutions in the United States. The Company invests in money market funds and high-grade, short-term commercial paper and corporate bonds, which management believes are subject to minimal credit and market risk.

Marketable Securities

Marketable securities consist of investments in high-grade corporate obligations, and government and government agency obligations that are classified as available-for-sale. Since these securities are available to fund current operations they are classified as current assets on the consolidated balance sheets.

The Company adjusts the cost of available-for-sale debt securities for amortization of premiums and accretion of discounts to maturity. The Company includes such amortization and accretion as a component of interest income, net. Realized gains and losses and declines in value, if any, that the Company judges to be other-than-temporary on available-for-sale securities are reported as a component of interest income, net. To determine whether an other-than-temporary impairment exists, the Company considers whether it intends to sell the debt security and, if the Company does not intend to sell the debt security, it considers available evidence to assess whether it is more likely than not that it will be required to sell the security before the recovery of its amortized cost basis. During the years ended December 31, 2018, 2017 and 2016, the Company determined it did not have any securities that were other-than-temporarily impaired.

Marketable securities are stated at fair value, including accrued interest, with their unrealized gains and losses included as a component of accumulated other comprehensive income or loss, which is a separate component of stockholders’ equity. The fair value of these securities is based on quoted prices and observable inputs on a recurring basis. Realized gains and losses are determined on the specific identification method. During the years ended December 31, 2018, 2017 and 2016, the Company did not have any realized gains or losses on marketable securities.

Fair Value of Financial Instruments

The carrying amounts of the Company’s financial instruments, which include cash equivalents, and marketable securities, approximate their fair values. The fair value of the Company’s financial instruments reflects the amounts that would be received upon sale of an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The fair value hierarchy has the following three levels:

Level 1—quoted prices in active markets for identical assets and liabilities.

Level 2—observable inputs other than Level 1 inputs. Examples of Level 2 inputs include quoted prices in active markets for similar assets or liabilities and quoted prices for identical assets or liabilities in markets that are not active.

Level 3—unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability.

Financial assets and liabilities are classified in their entirety within the fair value hierarchy based on the lowest level of input that is significant to the fair value measurement. The Company measures the fair value of its marketable securities by taking into consideration valuations obtained from third-party pricing sources. The pricing services utilize industry standard valuation models, including both income and market based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of and broker-dealer quotes on the same or similar securities, issuer credit spreads, benchmark securities and other observable inputs. As of December 31, 2018 and 2017, the Company’s financial assets valued based on Level 1 inputs consisted of cash and cash equivalents in a money market fund and its financial assets valued based on Level 2 inputs consisted of high-grade corporate bonds and commercial paper. During the years ended December 31, 2018, 2017 and 2016, the Company did not have any transfers of financials assets between Levels 1 and 2. As of December 31, 2018 and 2017, the Company did not have any financial liabilities that were recorded at fair value on a recurring basis on the balance sheet.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development costs are comprised of costs incurred in performing research and development activities, including internal costs (including stock-based compensation), costs for consultants, and other costs associated with the Company’s preclinical and clinical programs. In particular, Madrigal has conducted safety studies in animals, optimized and implemented the API manufacturing, and conducted Phase 1 & 2 clinical trials, all of which are considered research and development expenditures.

Patents

Costs to secure and defend patents are expensed as incurred and are classified as general and administrative expense in the Company’s statements of operations. Patent expenses were approximately $226 thousand, $176 thousand and $242 thousand for the years ended December 31, 2018, 2017 and 2016, respectively.

Stock-Based Compensation

The Company recognizes stock-based compensation expense based on the grant date fair value of stock options granted to employees, officers and directors. The Company uses the Black-Scholes option pricing model to determine the grant date fair value as management believes it is the most appropriate valuation method for its option grants. The Black-Scholes model requires inputs for risk-free interest rate, dividend yield, expected volatility and expected lives of the options. The expected lives for options granted represent the period of time that options granted are expected to be outstanding. The Company uses the simplified method for determining the expected lives of options. Expected volatility is based upon an industry estimate. The risk-free rate for periods within the expected life of the option is based on the U.S. Treasury yield curve in effect at the time of the grant. The Company estimates the forfeiture rate based on historical data. This analysis is re-evaluated at least annually and the forfeiture rate is adjusted as necessary.

Certain of the employee stock options granted by the Company are structured to qualify as incentive stock options (ISOs). Under current tax regulations, the Company does not receive a tax deduction for the issuance, exercise or disposition of ISOs if the employee meets certain holding requirements. If the employee does not meet the holding requirements, a disqualifying disposition occurs, at which time the Company may receive a tax deduction. The Company does not record tax benefits related to ISOs unless and until a disqualifying disposition is reported. In the event of a disqualifying disposition, the entire tax benefit is recorded as a reduction of income tax expense. The Company has not recognized any income tax benefit for its share-based compensation arrangements due to the fact that the Company does not believe it is more likely than not it will realize the related deferred tax assets.

Income Taxes

The Company uses the asset and liability method to account for income taxes. Deferred tax assets and liabilities are determined based on the expected future tax consequences of temporary differences between the Company’s financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse. The Company currently maintains a 100% valuation allowance on its deferred tax assets.

Comprehensive Loss

Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Changes in unrealized gains and losses on marketable securities represent the only difference between the Company's net loss and comprehensive loss.

Basic and Diluted Loss Per Common Share

Basic net loss per share is computed using the weighted average number of common shares outstanding during the period, excluding restricted stock that has been issued but is not yet vested. Diluted net loss per common share is computed using the weighted average number of common shares outstanding and the weighted average dilutive potential common shares outstanding using the treasury stock method. However, for the years ended December 31, 2018, 2017 and 2016, diluted net loss per share is the same as basic net loss per share as the inclusion of weighted average shares of unvested restricted common stock and common stock issuable upon the exercise of stock options would be anti-dilutive.

The following table summarizes outstanding securities not included in the computation of diluted net loss per common share as their inclusion would be anti-dilutive:


	As of December 31,
	2018	2017	2016
Common stock options	1,132,618	976,777	784,011
Unvested restricted common stock	52,063	104,127	157,262
Preferred stock	1,969,797	1,969,797	—

Recent Accounting Pronouncements

In June 2018, The Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2018-07, “Improvements to Nonemployee Share-Based Payment Accounting” to simplify the accounting for share-based payment transactions with non-employees of the Company. The guidance within this accounting standard update generally requires that share-based payment transactions for acquiring goods or services from non-employees of the Company be accounted for under the same guidance and model as all other share-based payment transactions, including employees of the Company. For public business entities, ASU 2018-07 is effective for annual and interim reporting periods beginning after December 15, 2018, with early adoption permitted. The Company elected to early adopt the guidance within this accounting standard update in the second quarter of 2018. There was no significant impact from the adoption.

In May 2017, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2017-09, “Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting,” to provide clarity and reduce both diversity in practice, and cost and complexity when a change is made to the terms or conditions of a share-based payment award. For public business entities, ASU 2017-09 is effective for annual and interim reporting periods beginning after December 15, 2017, with early adoption permitted. The update should be applied prospectively to an award modified on or after the adoption date. There was no significant impact from the adoption.

In March 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2016-09, “Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting,” which was designed to simplify several aspects of the accounting for share-based payment transactions, including, among other things, guidance related to accounting for income taxes, modification of the criteria for classification of awards as either equity awards or liability awards where an employer withholds shares from an employee’s share-based award for tax withholding purposes, and classification on the statement of cash flows of cash payments to a tax authority by an employer that withholds shares from an employee’s award for tax withholding purposes. The amendments in this ASU are effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods. The Company adopted ASU No. 2016-09 effective January 1, 2017. There was no significant impact from the adoption of ASU No. 2016-09 because the Company currently maintains a 100% valuation allowance on its deferred tax assets.

In August 2016, the FASB issued ASU No. 2016-15, “Statement of Cash Flows (Topic 230): Clarification of Certain Cash Receipts and Cash Payments.” The objective of ASU No. 2016-15 is to eliminate the diversity in practice related to the classification of certain cash receipts and payments in the statement of cash flows, by adding or clarifying guidance on eight specific cash flow issues. For public business entities, ASU 2016-15 is effective for annual and interim reporting periods beginning after December 15, 2017, with early adoption permitted. ASU 2015-16 provides that the amendments in the update should be applied retrospectively to all periods presented, unless deemed impracticable, in which case, prospective application is permitted. There was no significant impact from the adoption.

In January 2016, the FASB issued ASU No. 2016-01, “Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities,” which amends the guidance in U.S. generally accepted accounting principles on the classification and measurement of financial instruments. Changes to the current guidance primarily affect the accounting for equity investments, financial liabilities under the fair value option, and the presentation and disclosure requirements for financial instruments. In addition, the ASU clarifies guidance related to the valuation allowance assessment when recognizing deferred tax assets resulting from unrealized losses on available-for-sale debt securities. The amendments in this ASU are effective for fiscal years and interim periods beginning after December 15, 2017, and are to be adopted by means of a cumulative-effect adjustment to the balance sheet at the beginning of the first reporting period in which the guidance is effective. Early adoption is not permitted except for the provision to record fair value changes for financial liabilities under the fair value option resulting from instrument-specific credit risk in other comprehensive income. There was no significant impact from the adoption.

Reverse Merger

12 Months Ended

Dec. 31, 2018

Reverse Merger

Reverse Merger

3. Reverse Merger

On July 22, 2016, the Company, Synta and Saffron Merger Sub, Inc., a wholly-owned subsidiary of Synta (“Merger Sub”), completed their merger transaction pursuant to which Merger Sub merged with and into the Company with the Company becoming a wholly-owned subsidiary of Synta and the surviving corporation of the merger. Each outstanding share of private Madrigal common stock was converted into 0.1593 shares of common stock of the post-merger combined company. As a result, Synta issued 7.3 million shares of common stock to the stockholders of private Madrigal in exchange for common shares of private Madrigal. For accounting purposes, the Company is considered to be acquiring Synta in the merger. The Company was determined to be the accounting acquirer based upon the terms of the Merger Agreement and other factors including: (i) Madrigal security holders own approximately 64% of the voting interests of the combined company immediately following the closing of the merger; (ii) directors appointed by Madrigal hold a majority of board seats in the combined company; and (iii) Madrigal management hold a majority of the key positions in the management of the combined company. As the accounting acquirer, the Company’s assets and liabilities continue to be recorded at their historical carrying amounts and the historical operations that will be reflected in the financial statements will be those of the Company.

Immediately prior to the closing of the merger, Synta completed a one-for-35 reverse stock split. Following the reverse stock split and the merger, the post-merger combined company had approximately 11.3 million shares outstanding and the former stockholders of the Company owned approximately 64% of the outstanding capital stock of the post-merger combined company. The impact of the recapitalization of the Company has been retroactively applied to all periods presented.

Upon the closing of the merger transaction, the Company incurred an expense for a success fee of $750 thousand in cash, plus settled $750 thousand for both parties in shares of the post-merger combined company’s common stock with a third party financial advisor.

Purchase Price

Pursuant to the Merger Agreement, Synta issued to Madrigal stockholders a number of shares of Synta common stock representing approximately 64% of the outstanding shares of common stock of the combined company. The purchase price, which represents the consideration transferred to Synta stockholders in the reverse merger is calculated based on the number of shares of common stock of the combined company that Synta stockholders will own as of the closing of the merger, which consists of the following:



Number of shares of the combined company to be owned by Synta stockholders(1)		4,032,734
Multiplied by the fair value of Synta common stock(2)	$	9.48
Purchase price (in thousands)	$	38,236

(1)

Represents the number of shares of common stock of the combined company that Synta stockholders owned as of the closing of the merger pursuant to the Merger Agreement, including restricted stock awards and common stock underlying outstanding restricted stock units attributed to pre-combination services rendered by certain Synta employees and directors. This amount is calculated as 3,937,309 shares of Synta common stock outstanding as of July 22, 2016, including unvested restricted common stock, plus 95,425 shares of Synta common stock issuable pursuant to restricted stock units, net of tax withholdings, that vested immediately upon closing of the merger. The number of shares of common stock Synta issued to Madrigal stockholders was 7,253,655, calculated pursuant to the terms of the Merger Agreement based on Synta’s common stock outstanding as of July 22, 2016.

(2)

The fair value of Synta common stock used in determining the purchase price was $9.48, which was derived from the $0.2709 per share closing price of Synta common stock on July 21, 2016, the current price at the time of the closing, adjusted for the 1-for-35 reverse stock split.

Under the acquisition method of accounting, the total purchase price is allocated to the acquired tangible and intangible assets and assumed liabilities of Synta based on their estimated fair values as of the merger closing date. The excess of the purchase price over the fair value of assets acquired and liabilities assumed, if any, is allocated to goodwill. The allocation of the purchase price to the acquired assets and liabilities assumed of Synta based on the fair values as of July 22, 2016 is as follows, including measurement period adjustments since the fair values presented in the Company’s Form 10-Q for the quarter ended September 30, 2016 (in thousands):


			Measurement
			period	July 22 2016
	July 22, 2016		adjustments	(As adjusted)
Cash, cash equivalents and marketable securities	$	42,611		$	42,611
Prepaid expenses and other currents assets		1,715			1,715
Property and equipment, net		482	65		547
Accounts payable, accrued expenses and other liabilities		(7,019)			(7,019)
Term loans and capital lease obligations		(18)			(18)
In-process research and development		150	250		400
Goodwill		315	(315)		—
Net assets acquired	$	38,236		$	38,236

The Company’s measurement period adjustments were complete as of December 31, 2016. As a result of the measurement period adjustments recorded above, there was no gain or losses on the disposed tangible or intangible assets.

Convertible Promissory Notes-Related Parties

Immediately prior to the consummation of the merger, the September 14, 2011, September 16, 2011 and March 1, 2016 (amended and restated April 13, 2016) convertible note issuances outstanding totaling $47.6 million on July 22, including accrued but unpaid interest, were converted into 7.1 million shares of common stock on a post-split basis of the Company pursuant to their respective amended and restated terms (see Note 6).

Bonus Plan Awards

Pursuant to the terms of the Change in Control Bonus Plan, the participants therein received 0.6 million shares of common stock of the Company from certain former stockholders of the Company in connection with the merger, which represented 7.87% of Madrigal’s common shares outstanding at the time of the merger. The Company recorded $5.4 million in stock compensation associated with the transaction (see Note 9).

Stock Based Compensation

Following the consummation of the merger, the Company issued a combined 208,255 shares of restricted common stock and 557,386 stock options to purchase shares of common stock to the new Chief Executive Officer, Chief Medical Officer and Executive Vice President, Research and Development, and Chief Financial Officer and Senior Vice President.

Cash, Cash Equivalents and Marketable Securities

12 Months Ended

Dec. 31, 2018

Cash, Cash Equivalents and Marketable Securities

Cash, Cash Equivalents and Marketable Securities

5. Cash, Cash Equivalents and Marketable Securities

A summary of cash, cash equivalents and available-for-sale marketable securities held by the Company as of December 31, 2018, 2017 and 2016 is as follows (in thousands):


	December 31, 2018
			Unrealized		Unrealized		Fair
	Cost		gains		losses		value
Cash and cash equivalents:
Cash (Level 1)	$	2,004	$	—	$	—	$	2,004
Money market funds (Level 1)		43,401		—		—		43,401
Corporate debt securities due within 3 months of date of purchase (Level 2)		11,974		—		—		11,974
Total cash and cash equivalents		57,379		—		—		57,379
Marketable securities:
Corporate debt securities due within 1 year of date of purchase (Level 2)		426,658		14		(333)		426,339
Total cash, cash equivalents and marketable securities	$	484,037	$	14	$	(333)	$	483,718


	December 31, 2017
			Unrealized		Unrealized		Fair
	Cost		gains		losses		value
Cash and cash equivalents:
Cash (Level 1)	$	2,725	$	—	$	—	$	2,725
Money market funds (Level 1)		145,902		—		—		145,902
Corporate debt securities due within 3 months of date of purchase (Level 2)		—		—		—		—
Total cash and cash equivalents		148,627		—		—		148,627
Marketable securities:
Corporate debt securities due within 1 year of date of purchase (Level 2)		42,931		—		(31)		42,900
Total cash, cash equivalents and marketable securities	$	191,558	$	—	$	(31)	$	191,527


	December 31, 2016
			Unrealized		Unrealized		Fair
	Cost		gains		losses		value
Cash and cash equivalents:
Cash (Level 1)	$	5,651	$	—	$	—	$	5,651
Money market funds (Level 1)		13,494		—		—		13,494
Corporate debt securities due within 3 months of date of purchase (Level 2)		—		—		—		—
Total cash and cash equivalents		19,145		—		—		19,145
Marketable securities:
Corporate debt securities due within 1 year of date of purchase (Level 2)		21,330		25		—		21,355
Total cash, cash equivalents and marketable securities	$	40,475	$	25	$	—	$	40,500

Stockholders' Equity (Deficit)	12 Months Ended
Stockholders' Equity (Deficit)	Dec. 31, 2018
Stockholders' Equity (Deficit)
Stockholders' Equity (Deficit)	8. Stockholders’ Equity (Deficit) Common Stock Each common stockholder is entitled to one vote for each share of common stock held. The common stock will vote together with all other classes and series of stock of the Company as a single class on all actions to be taken by the Company’s stockholders. Each share of common stock is entitled to receive dividends, as and when declared by the Company’s board of directors. The Company has never declared cash dividends on its common stock and does not expect to do so in the foreseeable future. June 2018 Registered Offering of Common Stock In June 2018, the Company entered into an underwriting agreement with Goldman Sachs & Co. LLC, as representative of the several underwriters named therein (the “June 2018 Underwriters”), relating to an underwritten public offering (the “June 2018 Offering”) of 1,079,580 shares of the Company’s common stock, including 95,973 shares of the Company’s common stock purchased by the June 2018 Underwriters pursuant to a 30-day option to purchase such additional shares granted therein, at a public offering price of $305.00 per share. The June 2018 Offering resulted in gross proceeds to the Company of approximately $329.3 million, and net proceeds to the Company of approximately $311.8 million, after deducting the June 2018 Underwriters’ discount and other offering costs. The June 2018 Offering closed on June 11, 2018. December 2017 Registered Offering of Common Stock In December 2017, the Company entered into an underwriting agreement (the “Underwriting Agreement”) with Goldman Sachs & Co. LLC, as representative of the several underwriters named therein (the “Underwriters”), relating to an underwritten public offering (the “December 2017 Offering”) of 1,731,929 shares of the Company’s common stock, including 225,904 shares of the Company’s common stock purchased by the Underwriters pursuant to a 30-day option to purchase such additional shares granted therein, at a public offering price of $83.00 per share. The December 2017 Offering resulted in gross proceeds to the Company of approximately $143.8 million, and net proceeds to the Company of approximately $135.7 million, after deducting the Underwriters’ discount and other estimated offering expenses payable by the Company. The December 2017 Offering closed on December 21, 2017. June 2017 Private Placement Offering and Series A Convertible Preferred Stock In June 2017, the Company entered into a Securities Purchase Agreement (the “Purchase Agreement)” with a group of institutional accredited investors, who were existing, non-controlling stockholders of the Company, pursuant to which the Company sold securities to the Investors in a private placement transaction (the “June 2017 Offering”). Under the terms of the Purchase Agreement, the Company sold 328,300 shares of its common stock at a price of $15.23 per share, and 1,969,797 shares of its Series A Convertible Preferred Stock (the “Series A Preferred Stock”) at a price of $15.23 per share. The June 2017 Offering resulted in gross proceeds to the Company of approximately $35.0 million, and net proceeds to the Company of approximately $34.9 million. The June 2017 Offering closed on June 23, 2017. The Series A Preferred Stock has a par value of $0.0001 per share and is convertible into shares of the common stock at a one-to-one ratio, subject to adjustment as provided in the Purchase Agreement. The terms of the Series A Preferred Stock are set forth in the Certificate of Designation of Preferences, Rights and Limitations of Series A Convertible Preferred Stock, that the Company filed with the Secretary of State of the State of Delaware on June 21, 2017. Each share of the Series A Preferred Stock is convertible into shares of Common Stock at any time at the holder’s option. Upon any liquidation, dissolution or winding-up of the Company, whether voluntary or involuntary, after the satisfaction in full of the debts of the Company and the payment of any liquidation preference owed to the holders of shares of capital stock of the Company ranking prior to the Series A Preferred Stock upon liquidation, the holders of the Series A Preferred Stock shall participate pari passu with the holders of the Common Stock (on an as-if-converted-to-Common-Stock basis) in the net assets of the Company. Shares of the Series A Preferred Stock will generally have no voting rights, except as required by law. Shares of the Series A Preferred Stock will be entitled to receive dividends before shares of any other class or series of capital stock of the Company (other than dividends in the form of the Common Stock) equal to the dividend payable on each share of the Common Stock, on an as-converted basis. At-The-Market Issuance Sales Agreement In October 2015, the Company entered into an at-the-market issuance sales agreement (the “October 2015 Sales Agreement”), with Cowen and Company, LLC (“Cowen”), pursuant to which the Company may issue and sell shares of its common stock, having an aggregate offering price of up to $100 million, from time to time, at the Company’s option, through Cowen as its sales agent. Sales of common stock through Cowen may be made by any method that is deemed an “at-the-market” offering as defined in Rule 415 promulgated under the Securities Act of 1933, as amended, including by means of ordinary brokers’ transactions at market prices, in block transactions or as otherwise agreed by the Company and Cowen. Subject to the terms and conditions of the October 2015 Sales Agreement, Cowen will use commercially reasonable efforts consistent with its normal trading and sales practices to sell the common stock based upon the Company’s instructions (including any price, time or size limits or other customary parameters or conditions the Company may impose). The Company is not obligated to make any sales of its common stock under the October 2015 Sales Agreement. Any shares sold will be sold pursuant to an effective shelf registration statement on Form S-3 (file no. 333-206135). The Company will pay Cowen a commission of up to 3% of the gross proceeds. The October 2015 Sales Agreement may be terminated by the Company at any time upon 10 days’ notice. As of December 31, 2018, 597,256 shares have been sold under the October 2015 Sales Agreement for an aggregate of approximately $9.6 million in gross proceeds. Net proceeds to the Company were approximately $9.4 million after deducting commissions and other transactions costs. Of those shares sold, no shares were sold in 2018 and 215,539 shares were sold in 2017 for an aggregate of approximately $3.5 million in gross proceeds, and $3.4 million in net proceeds. Approximately $90.4 million remained reserved under the Company’s shelf registration statement and the applicable prospectus supplement for possible future issuance under the October 2015 Sales Agreement.

Stock-based Compensation

12 Months Ended

Dec. 31, 2018

Stock-based Compensation

Stock-based Compensation

9. Stock-based Compensation

In June 2015, upon obtaining stockholder approval at its annual shareholder meeting, the Company implemented its new 2015 Stock Plan. The 2015 Stock Plan replaced the 2006 Stock Plan which was terminated upon adoption of the 2015 Stock Plan. Shares of common stock reserved for outstanding awards under the 2006 Stock Plan that lapse or are cancelled will be added back to the share reserve available for future awards under the 2015 Stock Plan. The 2015 Stock Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock and other stock-based compensation awards to employees, officers, directors and consultants of the Company. The administration of the 2015 Stock Plan is under the general supervision of the compensation committee of the board of directors. The exercise price of the stock options is determined by the compensation committee of the board of directors, provided that incentive stock options are granted with an exercise price not less than fair market value of the common stock on the date of grant and expire no later than ten years from the date the option is granted. As of December 31, 2018, the Company had options outstanding to purchase 1,132,618 shares of its common stock, which includes options outstanding under its 2006 Stock Plan that was terminated in June 2015. As of December 31, 2018, 1,200,845 shares were available for future issuance.

The following table summarizes stock option activity during the twelve months ended December 31, 2018:


				Weighted
		Weighted		average	Aggregate
		average		remaining	intrinsic
		exercise		contractual	value (in
	Shares	price		life (years)	thousands)
Outstanding at January 1, 2018	976,777	$	11.97
Options granted	266,400		174.13
Options exercised	(101,809)		20.95
Options cancelled	(8,750)		113.81
Outstanding at December 31, 2018	1,132,618	$	48.52	8.01	$	89,086
Exercisable at December 31, 2018	623,657	$	12.31	7.59	$	63,221

The total cash received by the Company as a result of stock option exercises was $2.1 million in the year ended December 31, 2018 and $0.0 in each of the years ended December 31, 2017 and 2016. The total intrinsic value of options exercised was $18.8 million in the year ended December 31, 2018. The weighted-average grant date fair values, based on the Black-Scholes option model, of options granted during the year ended December 31, 2018, 2017 and 2016 was $137.49, $13.30 and $7.50, respectively.

Restricted Common Stock

The Company’s share-based compensation plan provides for awards of restricted shares of common stock to employees, officers, directors and consultants to the Company. Restricted stock awards are subject to forfeiture if employment or service terminates during the prescribed retention period. Restricted shares vest over the service period.

The following table summarizes unvested restricted share activity during the year ended December 31, 2018:


		Weighted
		average
		exercise
	Shares	price
Outstanding at January 1, 2018	104,127	$	9.45
Vested	(52,064)		9.45
Outstanding at December 31, 2018	52,063	$	9.45

Stock-Based Compensation Expense

Stock-based compensation expense during the years ended December 31, 2018, 2017 and 2016 was as follows (in thousands):



	Years Ended December 31,
	2018		2017		2016
Stock-based compensation expense by type of award:
Stock options	$	12,997	$	2,662	$	1,782
Restricted stock		492		592		736
Change in control bonus plan (see note 3)		—		—		5,411
Total stock-based compensation expense	$	13,489	$	3,254	$	7,929

Effect of stock-based compensation expense by line item:
Research and development	$	3,707	$	883	$	5,387
General and administrative		9,782		2,371		2,542
Total stock-based compensation expense included in net loss	$	13,489	$	3,254	$	7,929

Unrecognized stock-based compensation expense as of December 31, 2018 was as follows (in thousands):


			Weighted
	Unrecognized		average
	stock		remaining
	compensation		period
	expense		(in years)
Stock options	$	23,646	2.40
Restricted stock		272	0.55
Total	$	23,918	2.38

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Taxes

Income Taxes

12. Income Taxes

At December 31, 2018, the Company had federal net operating loss ("NOL") carryforwards of approximately $54.6 million and state operating loss carryforwards of approximately $43.3 million, available to reduce future taxable income, which expire between 2031 and 2037. The Company has unused federal research and development carryforwards of approximately $3.3 million which will begin to expire in 2031.

The Internal Revenue Code (“IRC”) limits the amounts of NOL carryforwards that a Company may use in any one year in the event of certain cumulative changes in ownership over a three-year period as described in Section 382 of the IRC. Such change in ownership could limit the Company’s utilization of the NOL, and could be triggered by subsequent sales of securities by the Company or stockholders. The deferred tax asset related to the NOL reflected on the financial statements could be affected by this limitation. Although a formal analysis has not been completed, the Company has determined that an ownership change likely occurred for Madrigal during the year ended December 31, 2017. The net operating losses are expected to be subject to an annual limitation; however, none of these NOLs is expected to expire before becoming available to reduce future taxable income.

The Company has analyzed the tax effect of the merger and concluded that an ownership change did take place for IRC 382 purposes. Based on the value of the business, Synta’s federal net operating losses and R&D credits are no longer available to be used by the Company. Further, the Company has concluded that the transaction did not trigger an ownership change for Madrigal.

In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some portion of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. As there is no assurance of future taxable income, a full valuation allowance has been established to offset the deferred tax assets. The valuation allowance increased $17.5 million for the year ended December 31, 2018. Changes in the deferred tax asset will be recorded as an income tax benefit or expense on the accompanying consolidated statements of operations.

Entities are also required to evaluate, measure, recognize and disclose any uncertain income tax provisions taken on their income tax returns. The Company has analyzed its tax positions and has concluded that as of December 31, 2018 there were no uncertain positions. The 2012 through 2017 tax returns are open to review by the IRS and state taxing authorities. Interest and penalties, if any, as they relate to income taxes assessed, are included in the income tax provision. There was no income tax related interest and penalties included in the income tax provision for 2018.

Temporary differences that give rise to deferred tax assets and liabilities are as follows (in thousands):


	For the years ended
	December 31,
	2018		2017		2016
Deferred Tax Liabilities
Stock Compensation	$	—	$	—	$	270
Unrealized Gains on Investments		—		—		13
Total Deferred Tax Liabilities	$	—	$	—	$	283
Deferred Tax Assets
Charitable Contributions	$	13	$	4	$	4
Accrued Expenses		498		421		—
Intangibles		477		579		997
Stock Compensation		4,395		605		—
Property, Plant & Equipment		9		—		—
Unrealized Loss on Investment		92		9		—
Net Operating Losses		14,851		9,229		12,749
Capitalized R&D		15,108		8,671		4,226
R&D Credit		3,505		1,901		846
Total deferred tax assets before valuation allowance		38,948		21,419		18,822
Valuation Allowance		(38,948)		(21,419)		(18,539)
Total deferred tax assets		—		—		283
Net deferred tax assets	$	—	$	—	$	—

Differences between the effective income tax rate and the US statutory rate were as follows (in thousands):


	For the years ended
	December 31,
	2018		2017		2016
Tax benefit at U.S. federal statutory rate	$	(6,890)	$	(10,592)	$	(8,972)
Non-deductible interest expenses		—		—		410
Stock based compensation		(3,415)		138		407
Transaction Costs		—		—		256
Effect of tax reform, change in federal tax rate		—		9,260		—
Other Nondeductible Expenses		—		1		1
State income taxes benefit before valuation allowance, net of federal benefit		(5,460)		(704)		(1,491)
Increase in domestic valuation allowance		17,529		2,880		9,750
Research and development credit		(1,604)		(825)		(390)
Other adjustments		(160)		(158)		29
Income tax expense (benefit)	$	—	$	—	$	—

Quarterly Financial Data (unaudited)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Data (unaudited)

Quarterly Financial Data (unaudited)

13. Quarterly Financial Data (unaudited)

The following tables present a summary of quarterly results of operations for 2018 and 2017 (in thousands, except shares and per share data):


	Three months ended
	March 31,		June 30,		September 30,		December 31,
	2018		2018		2018		2018
Revenues:
Total revenues	$	—	$	—	$	—	$	—
Operating expenses:
Research and development		5,198		5,109		6,211		8,871
General and administrative		1,871		2,717		5,122		5,583
Total operating expenses		7,069		7,826		11,333		14,454
Loss from operations		(7,069)		(7,826)		(11,333)		(14,454)
Interest expense		—		—		—		—
Interest income		705		1,166		2,821		2,979
Other income		—		200		—		—
Net loss	$	(6,364)	$	(6,460)	$	(8,512)	$	(11,475)
Net loss per common share:
Basic and diluted net loss per common share	$	(0.45)	$	(0.45)	$	(0.56)	$	(0.75)
Basic and diluted weighted average number of common shares outstanding		14,127,868		14,383,720		15,307,872		15,348,358


	Three months ended
	March 31,		June 30,		September 30,		December 31,
	2017		2017		2017		2017
Revenues:
Total revenues	$	—	$	—	$	—	$	—
Operating expenses:
Research and development		4,380		6,816		6,682		6,512
General and administrative		1,695		1,623		1,955		2,399
Total operating expenses		6,075		8,439		8,637		8,911
Loss from operations		(6,075)		(8,439)		(8,637)		(8,911)
Interest expense		—		—		—		—
Interest income		76		92		174		216
Other income		—		—		100		250
Net loss	$	(5,999)	$	(8,347)	$	(8,363)	$	(8,445)
Net loss per common share:
Basic and diluted net loss per common share	$	(0.50)	$	(0.69)	$	(0.68)	$	(0.67)
Basic and diluted weighted average number of common shares outstanding		11,955,739		12,039,005		12,378,622		12,597,864

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Summary of Significant Accounting Policies

Principle of Consolidation

Use of Estimates

Cash and Cash Equivalents

Marketable Securities

Fair Value of Financial Instruments

Level 1—quoted prices in active markets for identical assets and liabilities.

Level 3—unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability.

Research and Development Costs

Patents

Stock-Based Compensation

Income Taxes

Comprehensive Loss

Basic and Diluted Loss Per Common Share

The following table summarizes outstanding securities not included in the computation of diluted net loss per common share as their inclusion would be anti-dilutive:


	As of December 31,
	2018	2017	2016
Common stock options	1,132,618	976,777	784,011
Unvested restricted common stock	52,063	104,127	157,262
Preferred stock	1,969,797	1,969,797	—

Recent Accounting Pronouncements

Reverse Merger (Tables)

12 Months Ended

Dec. 31, 2018

Reverse Merger

Schedule of estimated purchase price



Number of shares of the combined company to be owned by Synta stockholders(1)		4,032,734
Multiplied by the fair value of Synta common stock(2)	$	9.48
Purchase price (in thousands)	$	38,236

(1)

(2)

Schedule of allocation of total purchase price to acquired assets and liabilities assumed

The allocation of the purchase price to the acquired assets and liabilities assumed of Synta based on the fair values as of July 22, 2016 is as follows, including measurement period adjustments since the fair values presented in the Company’s Form 10-Q for the quarter ended September 30, 2016 (in thousands):


			Measurement
			period	July 22 2016
	July 22, 2016		adjustments	(As adjusted)
Cash, cash equivalents and marketable securities	$	42,611		$	42,611
Prepaid expenses and other currents assets		1,715			1,715
Property and equipment, net		482	65		547
Accounts payable, accrued expenses and other liabilities		(7,019)			(7,019)
Term loans and capital lease obligations		(18)			(18)
In-process research and development		150	250		400
Goodwill		315	(315)		—
Net assets acquired	$	38,236		$	38,236

Cash, Cash Equivalents and Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2018

Cash, Cash Equivalents and Marketable Securities

Summary of cash, cash equivalents and available-for-sale marketable securities

A summary of cash, cash equivalents and available-for-sale marketable securities held by the Company as of December 31, 2018, 2017 and 2016 is as follows (in thousands):


	December 31, 2018
			Unrealized		Unrealized		Fair
	Cost		gains		losses		value
Cash and cash equivalents:
Cash (Level 1)	$	2,004	$	—	$	—	$	2,004
Money market funds (Level 1)		43,401		—		—		43,401
Corporate debt securities due within 3 months of date of purchase (Level 2)		11,974		—		—		11,974
Total cash and cash equivalents		57,379		—		—		57,379
Marketable securities:
Corporate debt securities due within 1 year of date of purchase (Level 2)		426,658		14		(333)		426,339
Total cash, cash equivalents and marketable securities	$	484,037	$	14	$	(333)	$	483,718


	December 31, 2017
			Unrealized		Unrealized		Fair
	Cost		gains		losses		value
Cash and cash equivalents:
Cash (Level 1)	$	2,725	$	—	$	—	$	2,725
Money market funds (Level 1)		145,902		—		—		145,902
Corporate debt securities due within 3 months of date of purchase (Level 2)		—		—		—		—
Total cash and cash equivalents		148,627		—		—		148,627
Marketable securities:
Corporate debt securities due within 1 year of date of purchase (Level 2)		42,931		—		(31)		42,900
Total cash, cash equivalents and marketable securities	$	191,558	$	—	$	(31)	$	191,527


	December 31, 2016
			Unrealized		Unrealized		Fair
	Cost		gains		losses		value
Cash and cash equivalents:
Cash (Level 1)	$	5,651	$	—	$	—	$	5,651
Money market funds (Level 1)		13,494		—		—		13,494
Corporate debt securities due within 3 months of date of purchase (Level 2)		—		—		—		—
Total cash and cash equivalents		19,145		—		—		19,145
Marketable securities:
Corporate debt securities due within 1 year of date of purchase (Level 2)		21,330		25		—		21,355
Total cash, cash equivalents and marketable securities	$	40,475	$	25	$	—	$	40,500

Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Stock-based Compensation

Summary of stock option activity

The following table summarizes stock option activity during the twelve months ended December 31, 2018:


				Weighted
		Weighted		average	Aggregate
		average		remaining	intrinsic
		exercise		contractual	value (in
	Shares	price		life (years)	thousands)
Outstanding at January 1, 2018	976,777	$	11.97
Options granted	266,400		174.13
Options exercised	(101,809)		20.95
Options cancelled	(8,750)		113.81
Outstanding at December 31, 2018	1,132,618	$	48.52	8.01	$	89,086
Exercisable at December 31, 2018	623,657	$	12.31	7.59	$	63,221

Summary of unvested restricted share activity

The following table summarizes unvested restricted share activity during the year ended December 31, 2018:


		Weighted
		average
		exercise
	Shares	price
Outstanding at January 1, 2018	104,127	$	9.45
Vested	(52,064)		9.45
Outstanding at December 31, 2018	52,063	$	9.45

Schedule of stock-based compensation expense

Stock-based compensation expense during the years ended December 31, 2018, 2017 and 2016 was as follows (in thousands):



	Years Ended December 31,
	2018		2017		2016
Stock-based compensation expense by type of award:
Stock options	$	12,997	$	2,662	$	1,782
Restricted stock		492		592		736
Change in control bonus plan (see note 3)		—		—		5,411
Total stock-based compensation expense	$	13,489	$	3,254	$	7,929

Effect of stock-based compensation expense by line item:
Research and development	$	3,707	$	883	$	5,387
General and administrative		9,782		2,371		2,542
Total stock-based compensation expense included in net loss	$	13,489	$	3,254	$	7,929

Schedule of unrecognized stock-based compensation expense

Unrecognized stock-based compensation expense as of December 31, 2018 was as follows (in thousands):


			Weighted
	Unrecognized		average
	stock		remaining
	compensation		period
	expense		(in years)
Stock options	$	23,646	2.40
Restricted stock		272	0.55
Total	$	23,918	2.38

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Taxes

Schedule of temporary differences that give rise to deferred tax assets and liabilities

Temporary differences that give rise to deferred tax assets and liabilities are as follows (in thousands):


	For the years ended
	December 31,
	2018		2017		2016
Deferred Tax Liabilities
Stock Compensation	$	—	$	—	$	270
Unrealized Gains on Investments		—		—		13
Total Deferred Tax Liabilities	$	—	$	—	$	283
Deferred Tax Assets
Charitable Contributions	$	13	$	4	$	4
Accrued Expenses		498		421		—
Intangibles		477		579		997
Stock Compensation		4,395		605		—
Property, Plant & Equipment		9		—		—
Unrealized Loss on Investment		92		9		—
Net Operating Losses		14,851		9,229		12,749
Capitalized R&D		15,108		8,671		4,226
R&D Credit		3,505		1,901		846
Total deferred tax assets before valuation allowance		38,948		21,419		18,822
Valuation Allowance		(38,948)		(21,419)		(18,539)
Total deferred tax assets		—		—		283
Net deferred tax assets	$	—	$	—	$	—

Schedule of differences between the effective income tax rate and the US statutory rate

Differences between the effective income tax rate and the US statutory rate were as follows (in thousands):


	For the years ended
	December 31,
	2018		2017		2016
Tax benefit at U.S. federal statutory rate	$	(6,890)	$	(10,592)	$	(8,972)
Non-deductible interest expenses		—		—		410
Stock based compensation		(3,415)		138		407
Transaction Costs		—		—		256
Effect of tax reform, change in federal tax rate		—		9,260		—
Other Nondeductible Expenses		—		1		1
State income taxes benefit before valuation allowance, net of federal benefit		(5,460)		(704)		(1,491)
Increase in domestic valuation allowance		17,529		2,880		9,750
Research and development credit		(1,604)		(825)		(390)
Other adjustments		(160)		(158)		29
Income tax expense (benefit)	$	—	$	—	$	—

Quarterly Financial Data (unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Data (unaudited)

Schedule of quarterly results of operations

The following tables present a summary of quarterly results of operations for 2018 and 2017 (in thousands, except shares and per share data):


	Three months ended
	March 31,		June 30,		September 30,		December 31,
	2018		2018		2018		2018
Revenues:
Total revenues	$	—	$	—	$	—	$	—
Operating expenses:
Research and development		5,198		5,109		6,211		8,871
General and administrative		1,871		2,717		5,122		5,583
Total operating expenses		7,069		7,826		11,333		14,454
Loss from operations		(7,069)		(7,826)		(11,333)		(14,454)
Interest expense		—		—		—		—
Interest income		705		1,166		2,821		2,979
Other income		—		200		—		—
Net loss	$	(6,364)	$	(6,460)	$	(8,512)	$	(11,475)
Net loss per common share:
Basic and diluted net loss per common share	$	(0.45)	$	(0.45)	$	(0.56)	$	(0.75)
Basic and diluted weighted average number of common shares outstanding		14,127,868		14,383,720		15,307,872		15,348,358


	Three months ended
	March 31,		June 30,		September 30,		December 31,
	2017		2017		2017		2017
Revenues:
Total revenues	$	—	$	—	$	—	$	—
Operating expenses:
Research and development		4,380		6,816		6,682		6,512
General and administrative		1,695		1,623		1,955		2,399
Total operating expenses		6,075		8,439		8,637		8,911
Loss from operations		(6,075)		(8,439)		(8,637)		(8,911)
Interest expense		—		—		—		—
Interest income		76		92		174		216
Other income		—		—		100		250
Net loss	$	(5,999)	$	(8,347)	$	(8,363)	$	(8,445)
Net loss per common share:
Basic and diluted net loss per common share	$	(0.50)	$	(0.69)	$	(0.68)	$	(0.67)
Basic and diluted weighted average number of common shares outstanding		11,955,739		12,039,005		12,378,622		12,597,864

Reverse Merger (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 22, 2016	Jul. 21, 2016	Dec. 31, 2018	Dec. 31, 2017
Reverse Merger
Common stock received			15,409,023	14,227,634
Shares outstanding			15,409,023	14,227,634
Merged Company
Reverse Merger
Success fee settled in cash	$ 750
Success fee settled for both parties in shares	$ 750
Merged Company \| Stockholders
Reverse Merger
Voting interest acquired	64.00%	64.00%
Merged Company
Reverse Merger
Number of shares issued for each share of private Madrigal stock	0.1593
Shares outstanding		11,300,000
Merged Company \| Synta Pharmaceuticals Corp
Reverse Merger
Number of shares of the combined company to be owned by Synta stockholders	4,032,734
Multiplied by the fair value of Synta common stock	$ 9.48
Purchase price	$ 38,236
Synta Pharmaceuticals Corp
Reverse Merger
Reverse stock split		0.02857
Multiplied by the fair value of Synta common stock		$ 9.48
Closing stock price (in dollars per share)		$ 0.2709
Synta Pharmaceuticals Corp \| Stockholders
Reverse Merger
Shares outstanding	3,937,309
Unvested restricted common stock	95,425
Synta Pharmaceuticals Corp \| Madrigal Pharmaceuticals, Inc
Reverse Merger
Common stock received	7,253,655

Reverse Merger - Allocation of Total Purchase Price (Details) - Synta Pharmaceuticals Corp - USD ($) $ in Thousands	5 Months Ended
	Dec. 31, 2016	Jul. 22, 2016
Allocation of the total purchase price to the acquired assets and liabilities assumed
Cash, cash equivalents and marketable securities	$ 42,611	$ 42,611
Prepaid expenses and other currents assets	1,715	1,715
Property and equipment, net	547	482
Accounts payable, accrued expenses and other liabilities	(7,019)	(7,019)
Term loans and capital lease obligations	(18)	(18)
In-process research and development	400	150
Goodwill		315
Net assets acquired	38,236	$ 38,236
Measurement period adjustments, Property and equipment, net	65
Measurement period adjustments, In-process research and development	250
Measurement period adjustments, Goodwill	(315)
Gain or losses on disposition of assets	$ 0

Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash, Cash Equivalents and Marketable Securities
Total cash, cash equivalents and marketable securities, Unrealized gains	$ 14		$ 25
Total cash, cash equivalents and marketable securities, Unrealized losses	(333)	$ (31)
Carrying value
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	57,379	148,627	19,145
Total cash, cash equivalents and marketable securities, Cost	484,037	191,558	40,475
Fair value
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	57,379	148,627	19,145
Total cash, cash equivalents and marketable securities, Fair value	$ 483,718	$ 191,527	$ 40,500
Corporate debt securities due within 3 months of date of purchase
Cash, Cash Equivalents and Marketable Securities
Maturity period from date of purchase to classify an investment as marketable securities	3 months	3 months	3 months
Corporate debt securities due within 3 months of date of purchase \| Carrying value \| Level 2
Cash, Cash Equivalents and Marketable Securities
Marketable securities, cost	$ 11,974
Corporate debt securities due within 3 months of date of purchase \| Fair value \| Level 2
Cash, Cash Equivalents and Marketable Securities
Marketable securities, fair value	$ 11,974
Corporate debt securities due within 1 year of date of purchase
Cash, Cash Equivalents and Marketable Securities
Maturity period from date of purchase to classify an investment as marketable securities	1 year	1 year	1 year
Corporate debt securities due within 1 year of date of purchase \| Level 2
Cash, Cash Equivalents and Marketable Securities
Marketable securities, unrealized gains	$ 14		$ 25
Marketable securities, unrealized losses	(333)	$ (31)
Corporate debt securities due within 1 year of date of purchase \| Carrying value \| Level 2
Cash, Cash Equivalents and Marketable Securities
Marketable securities, cost	426,658	42,931	21,330
Corporate debt securities due within 1 year of date of purchase \| Fair value \| Level 2
Cash, Cash Equivalents and Marketable Securities
Marketable securities, fair value	426,339	42,900	21,355
Cash \| Carrying value \| Level 1
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	2,004	2,725	5,651
Cash \| Fair value \| Level 1
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	2,004	2,725	5,651
Money market funds \| Carrying value \| Level 1
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	43,401	145,902	13,494
Money market funds \| Fair value \| Level 1
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	$ 43,401	$ 145,902	$ 13,494

Stockholders' Equity (Deficit) - June 2017 Private Placement (Details) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) Vote $ / shares shares	Dec. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($)
Stockholders' Equity (Deficit)
Value of shares sold by the entity \| $			$ 173,805
Net proceeds after deducting commissions and other transactions costs \| $		$ 311,825	$ 173,805	$ 5,954
Preferred Stock, Par or Stated Value Per Share \| $ / shares		$ 0.0001	$ 0.0001
Series A Convertible Preferred Stock
Stockholders' Equity (Deficit)
Preferred Stock, Par or Stated Value Per Share \| $ / shares	$ 0.0001
Preferred stock conversion ratio \| shares	1
Preferred shares number voting rights \| Vote	0
Private Placement Offering \| Purchase Agreement
Stockholders' Equity (Deficit)
Value of shares sold by the entity \| $	$ 35,000
Net proceeds after deducting commissions and other transactions costs \| $	$ 34,900
Private Placement Offering \| Common stock \| Purchase Agreement
Stockholders' Equity (Deficit)
Number of shares sold by the entity \| shares	328,300
Issue price of stock \| $ / shares	$ 15.23
Private Placement Offering \| Series A Convertible Preferred Stock \| Purchase Agreement
Stockholders' Equity (Deficit)
Number of shares sold by the entity \| shares	1,969,797
Issue price of stock \| $ / shares	$ 15.23

Stock-based Compensation - Stock Option (Details) - Stock options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based compensation expense
Shares available for future issuance	1,200,845
Shares
Outstanding at the beginning of the year (in shares)	976,777
Options granted (in shares)	266,400
Options exercised (in shares)	(101,809)
Options cancelled (in shares)	(8,750)
Outstanding at the end of the year (in shares)	1,132,618	976,777
Exercisable at the end of the year (in shares)	623,657
Weighted average exercise price
Outstanding at the beginning of the year (in dollars per share)	$ 11.97
Options granted (in dollars per share)	174.13
Options exercised (in dollars per share)	20.95
Options cancelled (in dollars per share)	113.81
Outstanding at the end of the year (in dollars per share)	48.52	$ 11.97
Exercisable at the end of the year (in dollars per share)	$ 12.31
Weighted average remaining contractual life (years)
Outstanding at the end of the year	8 years 4 days
Exercisable at the end of the year	7 years 7 months 2 days
Aggregate intrinsic value
Outstanding at the end of the year	$ 89,086
Exercisable at the end of the year	63,221
Additional disclosures
Total intrinsic value of options exercised	18,800
Proceeds resulting from exercise of stock options	$ 2,100	$ 0	$ 0
Weighted-average grant date fair value of options (in dollars per share)	$ 137.49	$ 13.30	$ 7.50
Maximum
Stock-based compensation expense
Expiration period	10 years

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Liabilities
Stock Compensation			$ 270
Unrealized Gains on Investments			13
Total Deferred Tax Liabilities			283
Deferred Tax Assets
Charitable Contributions	$ 13	$ 4	4
Accrued Expenses	498	421
Intangibles	477	579	997
Stock Compensation	4,395	605
Property, Plant & Equipment	9
Unrealized Loss on Investment	92	9
Net Operating Losses	14,851	9,229	12,749
Capitalized R&D	15,108	8,671	4,226
R&D Credit	3,505	1,901	846
Total deferred tax assets before valuation allowance	38,948	21,419	18,822
Valuation Allowance	$ (38,948)	$ (21,419)	(18,539)
Total deferred tax assets			$ 283

Income Taxes - Effective Income Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective income tax rate reconciliation
Tax benefit at U.S. federal statutory rate	$ (6,890)	$ (10,592)	$ (8,972)
Non-deductible interest expenses			410
Stock based compensation	(3,415)	138	407
Transaction Costs			256
Effect of tax reform, change in federal tax rate		9,260
Other Nondeductible Expenses		1	1
State income taxes benefit before valuation allowance, net of federal benefit	(5,460)	(704)	(1,491)
Increase in domestic valuation allowance	17,529	2,880	9,750
Research and development credit	(1,604)	(825)	(390)
Other adjustments	$ (160)	$ (158)	$ 29

Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating expenses:
Research and development	$ 8,871	$ 6,211	$ 5,109	$ 5,198	$ 6,512	$ 6,682	$ 6,816	$ 4,380	$ 25,389	$ 24,390	$ 15,933
General and administrative	5,583	5,122	2,717	1,871	2,399	1,955	1,623	1,695	15,293	7,672	9,290
Total operating expenses	14,454	11,333	7,826	7,069	8,911	8,637	8,439	6,075	40,682	32,062	25,223
Loss from operations	(14,454)	(11,333)	(7,826)	(7,069)	(8,911)	(8,637)	(8,439)	(6,075)	(40,682)	(32,062)	(25,223)
Interest expense											1,213
Interest income	2,979	2,821	1,166	705	216	174	92	76
Other income			200		250	100			200	350
Net loss	$ (11,475)	$ (8,512)	$ (6,460)	$ (6,364)	$ (8,445)	$ (8,363)	$ (8,347)	$ (5,999)	$ (32,811)	$ (31,154)	$ (26,388)
Basic and diluted net loss per common share (in dollars per share)	$ (0.75)	$ (0.56)	$ (0.45)	$ (0.45)	$ (0.67)	$ (0.68)	$ (0.69)	$ (0.50)	$ (2.22)	$ (2.54)	$ (5.07)
Basic and diluted weighted average number of common shares outstanding	15,348,358	15,307,872	14,383,720	14,127,868	12,597,864	12,378,622	12,039,005	11,955,739	14,796,712	12,244,939	5,204,644

Organization, Business and Basis of Presentation	12 Months Ended
Organization, Business and Basis of Presentation	Dec. 31, 2018
Organization, Business and Basis of Presentation
Organization, Business and Basis of Presentation	1. Organization, Business and Basis of Presentation Organization and Business Madrigal Pharmaceuticals, Inc. (the “Company” or “Madrigal”) is a clinical-stage pharmaceutical company developing novel, high-quality, small-molecule drugs addressing major unmet needs in cardiovascular, metabolic, and liver diseases. The Company’s lead compound, MGL-3196, is being advanced for non-alcoholic steatohepatitis (“NASH”), a liver disease that commonly affects people with metabolic diseases such as obesity and diabetes, and indications in dyslipidemia, potentially including genetic dyslipidemias such as familial hypercholesterolemia (“FH”). The Company initiated a Phase 2 study of MGL-3196 in NASH in October 2016. In February 2017, the Company initiated a Phase 2 study of MGL-3196 in patients with Heterozygous Familial Hypercholesterolemia (“HeFH”). Both Phase 2 studies were fully enrolled in 2017, the HeFH study was completed in February 2018, and the NASH study was completed in May 2018. Madrigal was originally incorporated as a private company (“Private Madrigal”) on August 19, 2011 and commenced operations in September 2011. On July 22, 2016, Private Madrigal completed a reverse merger (the “Merger”) into Synta Pharmaceuticals Corp. (“Synta”) (see Note 3). Upon the consummation of the Merger, the historical financial statements of Private Madrigal became the Company’s historical financial statements. Accordingly, the historical financial statements of Private Madrigal are included in the comparative prior periods. The Company, or Madrigal, as used in the accompanying notes to the consolidated financial statements, refers to Private Madrigal prior to the completion of the Merger and Public Madrigal subsequent to the completion of the Merger.

Liquidity and Uncertainties	12 Months Ended
Liquidity and Uncertainties	Dec. 31, 2018
Liquidity and Uncertainties
Liquidity and Uncertainties	4. Liquidity and Uncertainties The Company is subject to risks common to development stage companies in the Bio-Pharmaceutical industry including, but not limited to, uncertainty of product development and commercialization, dependence on key personnel, uncertainty of market acceptance of products and product reimbursement, product liability, uncertain protection of proprietary technology, potential inability to raise additional financing necessary for development and commercialization, and compliance with the U.S. Food and Drug Administration and other government regulations. The Company has incurred losses since inception, including approximately $32.8 million for the year ended December 31, 2018, resulting in an accumulated deficit of approximately $139.3 million and $106.5 million as of December 31, 2018 and 2017, respectively. Management expects to incur losses for the foreseeable future. To date, the Company has funded its operations primarily through the issuance of convertible debt (see Note 6), the proceeds from the Merger on July 22, 2016 (see Note 3), and proceeds from sales of the Company’s common and Series A Convertible Preferred Stock (see Note 8). The Company believes that its cash, cash equivalents and marketable securities at December 31, 2018 will be sufficient to fund operations past one year from the issuance of these financial statements. To meet its future capital needs, the Company intends to raise additional capital through debt or equity financings, collaborations, partnerships or other strategic transactions. However, there can be no assurance that the Company will be able to complete any such transactions on acceptable terms or otherwise. The inability of the Company to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s business, results of operations and financial condition. The Company has the ability to delay certain research activities and related clinical expenses if necessary due to liquidity concerns until a date in which those concerns are relieved.

Convertible Promissory Notes-Related Parties	12 Months Ended
Convertible Promissory Notes-Related Parties	Dec. 31, 2018
Convertible Promissory Notes-Related Parties
Convertible Promissory Notes-Related Parties	6. Convertible Promissory Notes—Related Parties Prior to the Merger, the Company was financed via issuances of convertible promissory notes, designated as “the September 14, 2011 Notes”, “the September 16, 2011 Notes”, and “the March 1, 2016 Notes”, respectively (collectively “the Notes”). The Notes accrued interest at 8% per annum, compounded monthly, and were collateralized by all assets of the Company. Effective April 13, 2016, in connection with execution of the Merger Agreement, the Notes were amended and restated, primarily to provide for mandatory conversion upon completion of the Merger. On that same date, the lenders collectively waived all accrued and unpaid interest under all of the convertible notes. The total accrued and waived interest amounted to $13.7 million. The lenders also agreed that no additional interest on these notes would be accrued through the date on which the Merger was consummated or terminated. Also on April 13, 2016, the Company reduced the convertible notes payable by the waived accrued interest less $2.5 million of accrued interest for the period April 14, 2016 through the maturity date of December 31, 2016, as required under Troubled Debt Restructuring accounting guidance. The net waived interest of $11.2 million was recorded as an increase in Additional Paid in Capital (“APIC”) at the time of the amendment, as the notes were held by related parties. The remaining $2.5 million of accrued interest was recorded as an increase in APIC upon conversion at the Merger. During the period March 1, 2016 through the Merger, the lenders provided convertible promissory note financing of $8.5 million in cash. Additionally, on April 13, 2016, one of the lenders exchanged $0.5 million of Advances Payable for an equal amount of convertible promissory notes.

Advances Payable-Related Party	12 Months Ended
Advances Payable-Related Party	Dec. 31, 2018
Advances Payable-Related Party
Advances Payable-Related Party	7. Advances Payable—Related Party On June 29, 2015 and July 30, 2015 a related party agreed to advance the Company a total of $500 thousand to be used for working capital requirements. The advances accrued interest at a rate of four percent (4%) per annum compounded annually. On April 13, 2016, these advances were exchanged for $500 thousand in convertible promissory notes payable and all accrued interest was waived (see Note 6).

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2018
Related Party Transactions
Related Party Transactions	10. Related Party Transactions Related Party Financing For the years ended December 31, 2018, 2017 and 2016, the Company incurred approximately $0.0, $0.0 and $1.2 million, respectively of interest expense to related party lenders which was subsequently waived (see Note 6). This debt was converted to equity at the time of the Merger. Consulting Agreement The Company had a consulting agreement with its former Chief Executive Officer (“CEO”), who is also a stockholder of the Company. The consulting agreement automatically renewed monthly unless terminated. The consulting agreement could be terminated upon fifteen (15) day notice by the Company or the CEO. The consultant was paid $0 for the years ended December 31, 2018 and 2017, respectively, and $93 thousand for the year ended December 31, 2016. On July 22, 2016, this consulting agreement was replaced by an employment agreement for the position of Chief Medical Officer (“CMO”) upon the completion of the Merger (see Note 3).

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Consolidated Balance Sheets
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	1,969,797	1,969,797
Preferred stock, shares outstanding	1,969,797	1,969,797
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	15,409,023	14,227,634
Common stock, shares outstanding	15,409,023	14,227,634

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2018
Commitments and Contingencies
Commitments and Contingencies	11. Commitments and Contingencies The Company has a Research, Development and Commercialization Agreement with Hoffmann-La Roche (“Roche”) which grants the Company a sole and exclusive license to develop, use, sell, offer for sale and import any Licensed Product as defined by the agreement. The agreement requires future milestone payments to Roche, the remainder of which total $10 million and are earned by the commencement of Phase 3 clinical trials as well as future regulatory approval in the United States and Europe of a product developed from MGL-3916. A single-digit royalty payment range is based on net sales of products developed from MGL-3196, subject to certain reductions. In October 2016 the Company commenced a Phase 2 study in Non-Alcoholic Steatohepatitis (NASH), which triggered a milestone payment under the agreement. Except as described above, the Company has not achieved any additional product development or regulatory milestones to date and has no Licensed Product sales for the years ended December 31, 2018, 2017 and 2016. During 2018, the Company has entered into several customary contractual arrangements and letters of intent in preparation for and in support of the Phase 2 and 3 clinical trials.

Summary of Significant Accounting Policies - Income Taxes (Details)	12 Months Ended
	Dec. 31, 2018
Income Taxes
Valuation allowance on deferred tax assets (as a percent)	100.00%

Convertible Promissory Notes-Related Parties (Details) $ in Thousands			1 Months Ended	5 Months Ended	12 Months Ended
	Jul. 22, 2016 USD ($)	Apr. 13, 2016 USD ($) Lender	Jul. 30, 2015	Jul. 22, 2016 USD ($)	Dec. 31, 2018	Dec. 31, 2016 USD ($)
Interest rate			4.00%
Cash received						$ 8,500
Conversion amount						500
Amended And Restated March 1, 2016 Notes
Cash received				$ 8,500
Convertible Promissory Notes
Interest rate					8.00%
Total accrued and waived interest		$ 13,700
Accrued interest						$ 2,500
Net waived interest recorded as an increase to APIC		11,200
Accrued interest recorded as increase in APIC upon conversion	$ 2,500
Conversion amount		$ 500
Lender D \| Amended And Restated March 1, 2016 Notes
Number of lender that exchanged advances payable to convertible debt \| Lender		1
Conversion amount		$ 500

Advances Payable-Related Party (Details) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	Apr. 13, 2016	Jul. 30, 2015	Dec. 31, 2018	Dec. 31, 2016
Advances Payable-Related Party
Working capital requirements		$ 500
Interest rate of advances from related party		4.00%
Exchange of related party advances payable for convertible notes				$ 500
Convertible Promissory Notes
Advances Payable-Related Party
Interest rate of advances from related party			8.00%
Exchange of related party advances payable for convertible notes	$ 500

Stockholders' Equity (Deficit) - Common Stock (Details)	12 Months Ended
Stockholders' Equity (Deficit) - Common Stock (Details)	Dec. 31, 2018 Vote
Stockholders' Equity (Deficit)
Number of votes per share that common stockholders are entitled to receive	1

Stockholders' Equity (Deficit) - At The Market Issuances (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended		39 Months Ended
	Oct. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018
Stockholders' Equity (Deficit)
Value of shares sold by the entity			$ 173,805
At-The-Market Issuance Sales Agreement
Stockholders' Equity (Deficit)
Number of shares sold by the entity		0	215,539	597,256
Value of shares sold by the entity			$ 3,500	$ 9,600
Net proceeds after deducting commissions and other transactions costs			$ 3,400	9,400
Remaining reserved amount under shelf registration		$ 90,400		$ 90,400
Cowen & Co. LLC \| At-The-Market Issuance Sales Agreement
Stockholders' Equity (Deficit)
Notice period of termination of sales agreement	10 days
Cowen & Co. LLC \| Maximum \| At-The-Market Issuance Sales Agreement
Stockholders' Equity (Deficit)
Maximum aggregate offering price	$ 100,000
Percentage of gross proceeds payable as commission	3.00%

Stock-based Compensation - Restricted Common Stock (Details) - Unvested restricted common stock	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Shares
Outstanding at January 1, 2018 \| shares	104,127
Vested (in shares) \| shares	(52,064)
Outstanding at December 31, 2018 \| shares	52,063
Weighted average grant date fair value
Outstanding at January 1, 2018 (in dollars per share) \| $ / shares	$ 9.45
Vested (in dollars per share) \| $ / shares	9.45
Outstanding at December 31, 2018 (in dollars per share) \| $ / shares	$ 9.45

Stock-based Compensation - Unrecognized Expense (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Unrecognized stock-based compensation expense
Unrecognized stock compensation expense	$ 23,918
Weighted average remaining period (in years)	2 years 4 months 17 days
Stock options
Unrecognized stock-based compensation expense
Unrecognized stock compensation expense	$ 23,646
Weighted average remaining period (in years)	2 years 4 months 24 days
Unvested restricted common stock
Unrecognized stock-based compensation expense
Unrecognized stock compensation expense	$ 272
Weighted average remaining period (in years)	6 months 18 days

Income Taxes - Net Operating Loss Carryforwards (Details) $ in Millions	Dec. 31, 2018 USD ($)
Federal
Income Taxes
Net operating loss	$ 54.6
State
Income Taxes
Net operating loss	$ 43.3

Income Taxes - Research and Development Carryforward (Details) $ in Millions	Dec. 31, 2018 USD ($)
Federal \| Research and development carryforward
Income Taxes
Research and development tax credit carryforwards	$ 3.3

Income Taxes - Valuation Allowance and Uncertain Tax Position (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Income Taxes
Increase in valuation allowance	$ 17.5
Liability for uncertain tax positions	0.0
Income tax related interest and penalties	$ 0.0