Esperion Therapeutics (ESPR) 10-K 27 Feb 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Feb. 01, 2020	Jun. 28, 2019
Document and Entity Information
Entity Registrant Name	Esperion Therapeutics, Inc.
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	001-35986
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-1870780
Entity Address, Address Line One	3891 Ranchero Drive, Suite 150
Entity Address, City or Town	Ann Arbor
Entity Address, State or Province	MI
Entity Address, Postal Zip Code	48108
City Area Code	734
Local Phone Number	887-3903
Title of 12(b) Security	Common Stock
Trading Symbol	ESPR
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 1,090
Entity Common Stock, Shares Outstanding		27,512,441
Entity Central Index Key	0001434868
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 166,130	$ 36,973
Restricted cash	928
Short-term investments	34,651	99,050
Prepaid clinical development costs	6,081	5,275
Other prepaid and current assets	3,924	1,334
Total current assets	211,714	142,632
Property and equipment, net	1,145	520
Intangible assets	56	56
Long-term investments		243
Right of use operating lease assets	1,532
Total assets	214,447	143,451
Current liabilities:
Accounts payable	28,856	44,893
Accrued clinical development costs	17,511	16,039
Other accrued liabilities	11,871	3,401
Revenue interest liability	5,236
Deferred revenue from collaborations	2,152
Operating lease liabilities	454
Total current liabilities	66,080	64,333
Revenue interest liability	127,308
Operating lease liabilities	1,109
Total liabilities	194,497	64,333
Commitments and contingencies (Note 5)
Stockholders' equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized and no shares issued or outstanding as of December 31, 2019 and December 31, 2018
Common stock, $0.001 par value; 120,000,000 shares authorized as of December 31, 2019 and December 31, 2018; 27,497,911 shares issued and outstanding at December 31, 2019 and 26,824,859 shares issued and outstanding at December 31, 2018	27	27
Additional paid-in capital	715,166	677,511
Accumulated other comprehensive gain (loss)	23	(319)
Accumulated deficit	(695,266)	(598,101)
Total stockholders' equity	19,950	79,118
Total liabilities and stockholders' equity	$ 214,447	$ 143,451

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Balance Sheets
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	27,497,911	26,824,859
Common stock, shares outstanding	27,497,911	26,824,859

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Total Revenues	$ 148,364
Type of Revenue	espr:CollaborationRevenueMember
Operating expenses:
Research and development	$ 175,611	$ 171,488	$ 147,603
General and administrative	65,854	33,097	21,379
Total operating expenses	241,465	204,585	168,982
Loss from operations	(93,101)	(204,585)	(168,982)
Interest expense	(8,120)	(28)	(198)
Other income, net	4,056	2,803	2,192
Net loss	$ (97,165)	$ (201,810)	$ (166,988)
Net loss per common share (basic and diluted)	$ (3.59)	$ (7.54)	$ (6.98)
Weighted-average shares outstanding (basic and diluted)	27,090,284	26,754,308	23,933,273
Other comprehensive gain (loss):
Unrealized gain (loss) on investments	$ 342	$ 526	$ (673)
Total comprehensive loss	$ (96,823)	$ (201,284)	$ (167,661)

Statements of Stockholders' Equ

Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Total
Balance at Dec. 31, 2016	$ 23	$ 457,951	$ (229,200)	$ (172)	$ 228,602
Balance (in shares) at Dec. 31, 2016	22,555,413
Increase (Decrease) in Stockholders' Equity
Adoption of accounting standard 2016-09		103	(103)
Issuance of common stock from public offering, net of issuance costs ($226)	$ 3	163,975			163,978
Issuance of common stock from public offering, net of issuance costs (in shares)	3,565,000
Exercise of stock options		1,167			1,167
Exercise of stock options (in shares)	115,483
Exercise of warrants (in shares)	62,525
Vesting of restricted stock units (in shares)	6,248
Stock-based compensation		18,605			18,605
Other comprehensive gain (loss)				(673)	(673)
Net loss			(166,988)		(166,988)
Balance at Dec. 31, 2017	$ 26	641,801	(396,291)	(845)	244,691
Balance (in shares) at Dec. 31, 2017	26,304,669
Increase (Decrease) in Stockholders' Equity
Exercise of stock options	$ 1	11,742			11,743
Exercise of stock options (in shares)	356,809
Exercise of warrants (in shares)	159,944
Vesting of restricted stock units (in shares)	3,437
Stock-based compensation		23,968			23,968
Other comprehensive gain (loss)				526	526
Net loss			(201,810)		(201,810)
Balance at Dec. 31, 2018	$ 27	677,511	(598,101)	(319)	$ 79,118
Balance (in shares) at Dec. 31, 2018	26,824,859				26,824,859
Increase (Decrease) in Stockholders' Equity
Exercise of stock options		11,771			$ 11,771
Exercise of stock options (in shares)	649,529				649,529
Exercise of warrants (in shares)	5,813
Vesting of restricted stock units (in shares)	17,710
Stock-based compensation		25,884			$ 25,884
Other comprehensive gain (loss)				342	342
Net loss			(97,165)		(97,165)
Balance at Dec. 31, 2019	$ 27	$ 715,166	$ (695,266)	$ 23	$ 19,950
Balance (in shares) at Dec. 31, 2019	27,497,911				27,497,911

Statements of Stockholders' E_2

Statements of Stockholders' Equity (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Statements of Stockholders' Equity
Stock issuance costs paid and offering costs not yet paid	$ 226

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net loss	$ (97,165)	$ (201,810)	$ (166,988)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	319	265	258
Amortization (accretion) of premiums and discounts on investments	(200)	(217)	334
Non-cash interest expense related to the revenue interest liability	8,120
Stock-based compensation expense	25,884	23,968	18,605
Changes in assets and liabilities:
Prepaids and other assets	(3,396)	(2,884)	(1,731)
Deferred revenue	2,152
Accounts payable	(16,055)	24,446	15,758
Other accrued liabilities	10,000	7,594	2,462
Net cash used in operating activities	(70,341)	(148,638)	(131,302)
Investing activities
Purchases of investments	(34,326)	(25,481)	(219,577)
Proceeds from sales/maturities of investments	99,510	166,081	183,743
Purchase of property and equipment	(953)	(151)	(19)
Net cash provided by (used in) investing activities	64,231	140,449	(35,853)
Financing activities
Proceeds from issuance of common stock, net of issuance costs			164,000
Proceeds from revenue interest liability, net of issuance costs	124,424
Proceeds from exercise of common stock options	11,771	11,743	1,167
Payments on long-term debt		(1,049)	(1,709)
Net cash provided by financing activities	136,195	10,694	163,458
Net increase (decrease) in cash, cash equivalents, and restricted cash	130,085	2,505	(3,697)
Cash and cash equivalents at beginning of period	36,973	34,468	38,165
Cash, cash equivalents and restricted cash at end of period	167,058	36,973	34,468
Supplemental disclosure of cash flow information:
Purchase of property and equipment not yet paid	190	$ 199
Non cash right of use asset	$ 31
Offering costs not yet paid			$ 22

The Company and Basis of Presen

The Company and Basis of Presentation	12 Months Ended
	Dec. 31, 2019
The Company and Basis of Presentation
The Company and Basis of Presentation	1. The Company and Basis of Presentation The Company is the Lipid Management Company, a pharmaceutical company focused on developing and commercializing affordable, oral, once-daily, non-statin medicines for the treatment of patients with elevated low density lipoprotein cholesterol ("LDL-C"). Through scientific and clinical excellence, and a deep understanding of cholesterol biology, the experienced Lipid Management Team at Esperion is committed to developing new LDL-C lowering medicines that will make a substantial impact on reducing global cardiovascular disease ("CVD"); the leading cause of death around the world. NEXLETOL TM TM On February 21, 2020, the Company announced that the U.S. Food and Drug Administration (“FDA”) approved NEXLETOL an adjunct to diet and maximally tolerated statin therapy for the treatment of adults with HeFH or established ASCVD who require additional lowering of LDL-C. The effect of NEXLETOL on cardiovascular morbidity and mortality has not been determined. NEXLETOL is the first oral, once-daily, non-statin LDL-C lowering medicine approved since 2002 for indicated patients. On February 26, 2020, the Company announced that the FDA approved NEXLIZET indicated as an adjunct to diet and maximally tolerated statin therapy for the treatment of adults with HeFH or established ASCVD who require additional lowering of LDL-C. The effect of NEXLIZET on cardiovascular morbidity and mortality has not been determined. NEXLIZET is the first non-statin, LDL-C lowering combination medicine ever approved. Bempedoic acid and the bempedoic acid / ezetimibe combination tablet are under regulatory review by the European Medicines Agency (“EMA”). The two Marketing Authorisation Applications (“ MAAs”), will be applicable to all 28 European Union member states plus the United Kingdom, Iceland, Norway and Liechtenstein. On January 31, 2020, the Committee for Medicinal Products for Human Use (“CHMP”) of the EMA adopted a positive opinion for the MAAs of both bempedoic acid and the bempedoic acid / ezetimibe combination tablet, recommending approval for the treatment of hypercholesterolemia and mixed dyslipidemia. The European Commission will review the CHMP opinion and is expected to deliver its final decision in April 2020. The Company is conducting a global cardiovascular outcomes trial ("CVOT")—known as C L E A R The Company's primary activities since incorporation have been conducting research and development activities, including nonclinical, preclinical and clinical testing, performing business and financial planning, recruiting personnel, and raising capital. Accordingly, the Company has not commenced principal operations and only received approval to sell NEXLETOL and NEXLIZET in February 2020. The Company is subject to risks and uncertainties which include the need to research, develop, and clinically test potential therapeutic products; obtain regulatory approvals for its products and commercialize them, if approved; expand its management and scientific staff; and finance its operations with an ultimate goal of achieving profitable operations. ​ 1. The Company and Basis of Presentation (Continued) The Company has sustained annual operating losses since inception and expects such losses to continue over the foreseeable future. While management believes current cash resources and future cash received from the Company's collaboration agreement with Daiichi Sankyo Europe GmbH ("DSE"), entered into on January 2, 2019, and from the Revenue Interest Purchase Agreement (“RIPA”) with Eiger III SA LLC (“Oberland”), an affiliate of Oberland Capital LLC, and the Purchasers named therein, entered into on June 26, 2019, will fund operations for the foreseeable future, management may continue to fund operations and advance the development of the Company's product candidates through a combination of collaborations with third parties, strategic alliances, licensing arrangements, permitted debt financings, permitted royalty-based financings, and permitted private and public and equity offerings or through other sources. If adequate funds are not available, the Company may not be able to continue the development of its current or future product candidates, or to commercialize its current or future product candidates, if approved.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in accordance with generally accepted accounting principles in the United States requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, expenses and related disclosures. Actual results could differ from those estimates. Cash and Cash Equivalents The Company invests its excess cash in bank deposits, money market accounts, and short-term investments. The Company considers all highly liquid investments with an original maturity of 90 days or less at the time of purchase to be cash equivalents. Cash equivalents are reported at fair value. Restricted Cash Restricted cash consists of legally restricted amounts held by financial institutions pursuant to contractual arrangements. Investments Investments are considered to be available-for-sale and are carried at fair value. Unrealized gains and losses, if any, are reported as a separate component of stockholders’ equity. The cost of investments classified as available-for-sale are adjusted for the amortization of premiums and accretion of discounts to maturity and recorded in other income, net. Realized gains and losses, if any, are determined using the specific identification method and recorded in other income, net. Investments with original maturities beyond 90 days at the date of purchase and which mature at, or less than twelve months from, the balance sheet date are classified as current. Investments with a maturity beyond twelve months from the balance sheet date are classified as long-term. Concentration of Credit Risk Cash, cash equivalents, and marketable securities consist of financial instruments that potentially subject the Company to concentrations of credit risk. The Company has established guidelines for investment of its excess cash and believes the guidelines maintain safety and liquidity through diversification of counterparties and maturities. Segment Information The Company views its operations and manages its business in one operating segment, which is the business of researching, developing and commercializing therapies for the treatment of patients with elevated LDL-C. ​ 2. Summary of Significant Accounting Policies (Continued) Fair Value of Financial Instruments The Company’s cash, cash equivalents, restricted cash and investments are carried at fair value. Financial instruments, including other prepaid and current assets, accounts payable and accrued liabilities are carried at cost, which approximates fair value. Debt is carried at amortized cost, which approximates fair value. Property and Equipment, Net Property and equipment are recorded at cost, less accumulated depreciation. Depreciation is provided using the straight-line method over the estimated useful lives of the respective assets, generally three to ten years . Leasehold improvements are amortized over the lesser of the lease term or the estimated useful lives of the related assets. Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. The impairment loss, if recognized, would be based on the excess of the carrying value of the impaired asset over its respective fair value. No impairment losses have been recorded through December 31, 2019. Leases The Company reviews all arrangements to determine if the contract contains a lease or an embedded lease using the criteria in Accounting Standards Codification ("ASC") 842. If a lease is identified, the Company reviews the consideration in the contract and separates the lease components from the nonlease components. In addition, the Company reviews the classification of the lease between operating and finance leases. According to ASC 842, lessees should discount lease payments at the lease commencement date using the rate implicit in the lease. If the rate implicit in the lease is not readily determinable, a lessee must use its incremental borrowing rate for purposes of classifying the lease and measuring the right-of-use asset and liability. To the extent the rate is not implicit in the lease, the Company uses the incremental borrowing rate it would have to pay to borrow on a collateralized basis over a similar term in an amount equal to the lease payments in a similar economic environment. Revenue Interest Liability The revenue interest liability is presented net of deferred issuance costs on the balance sheets. The Company imputes interest expense associated with this liability using the effective interest rate method. The effective interest rate is calculated based on the rate that would enable the debt to be repaid in full over the anticipated life of the arrangement. The interest rate on the liability may vary during the term of the agreement depending on a number of factors, including the level of forecasted net sales. The Company evaluates the interest rate quarterly based on its current net sales forecasts utilizing the prospective method. Revenue Recognition a. Collaboration Revenue The Company has entered into an agreement related to its activities to develop, manufacture, and commercialize its product candidates. The Company earns collaboration revenue in connection with a collaboration agreement to develop and/or commercialize product candidates where the Company deems the collaborator to be the customer. The Company has adopted ASC 606, Revenue from Contracts with Customers, and under the terms of the standard, revenue is measured as the amount of consideration expected to be entitled to in exchange for transferring promised goods or providing services to a customer. Revenue is recognized when (or as) the Company satisfies performance obligations ​ 2. Summary of Significant Accounting Policies (Continued) under the terms of a contract. Depending on the terms of the arrangement, the Company may defer the recognition of all or a portion of the consideration received as the performance obligations are satisfied. The collaboration agreement may require the Company to deliver various rights, services, and/or goods across the entire life cycle of a product or product candidate. In the agreement involving multiple goods or services promised to be transferred to a customer, the Company must assess, at the inception of the contract, whether each promise represents a separate performance obligation (i.e., is "distinct"), or whether such promises should be combined as a single performance obligation. The terms of the agreement typically include consideration to be provided to the Company in the form of non-refundable up-front payments, development milestones, sales milestones, and royalties on sales of products within a respective territory. At the inception of the contract, the transaction price reflects the amount of consideration the Company expects to be entitled to in exchange for transferring promised goods or services to its customer. In the arrangement where the Company satisfies performance obligation(s) during the regulatory phase over time, the Company recognizes collaboration revenue typically using an input method on the basis of regulatory costs incurred relative to the total expected cost which determines the extent of progress toward completion. The Company reviews the estimate of the transaction price and the total expected cost each period, and makes revisions to such estimates as necessary. Under the Company's collaboration agreement, product sales and cost of sales may be recorded by the Company's collaborators as they are deemed to be the principal in the transaction. The Company receives royalties from the commercialization of such products, and records its share of the variable consideration, representing a percentage of net product sales, as collaboration revenue in the period in which such underlying sales occur and costs are incurred by the collaborator. The collaborator will provide the Company with estimates of its royalties for such quarter; these estimates are reconciled to actual results in the subsequent quarter, and the royalty is adjusted accordingly, as necessary. Please refer to the discussion in Note 3 "Collaborations with Third Parties" for further discussion of the accounting related to the collaboration agreement. Research and Development Research and development expenses consist of costs incurred to further the Company’s research and development activities and include salaries and related benefits, costs associated with clinical activities, nonclinical activities, regulatory activities, manufacturing activities to support clinical activities and commercial product manufacturing supply as the Company approaches anticipated approval, research-related overhead expenses and fees paid to external service providers that conduct certain research and development, clinical, and manufacturing activities on behalf of the Company. Research and development costs are expensed as incurred. Accrued Clinical Development Costs Outside research costs are a component of research and development expense. These expenses include fees paid to clinical research organizations and other service providers that conduct certain clinical and product development activities on behalf of the Company. Depending upon the timing of payments to the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These accrued or prepaid expenses are based on management’s estimates of the work performed under service agreements, milestones achieved and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly. Income Taxes The Company utilizes the liability method of accounting for income taxes as required by ASC 740, Income Taxes. Under this method, deferred tax assets and liabilities are determined based on differences between financial reporting ​ 2. Summary of Significant Accounting Policies (Continued) and the tax basis of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company has incurred annual operating losses since inception. Accordingly, it is not more likely than not that the Company will realize a tax benefit from its deferred tax assets and as such, it has recorded a full valuation allowance. Stock-Based Compensation The Company accounts for stock-based compensation in accordance with the provisions of ASC 718, Compensation—Stock Compensation. Accordingly, compensation costs related to equity instruments granted are recognized over the requisite service periods of the awards on a straight-line basis at the grant-date fair value calculated using a Black-Scholes option-pricing model. The Company accounts for forfeitures as they occur. Expense is recognized during the period the related services are rendered. Recent Accounting Pronouncements In November 2018, the Financial Accounting Standards Board ("FASB") issued Accounting Standard Update ("ASU") 2018-08, which clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606 when the collaborative arrangement participant is a customer in the context of a unit of account. The standard is effective for public companies for fiscal years beginning after December 15, 2019, and interim periods within those years. Early adoption is permitted, included in any interim period, provided an entity has already adopted ASC 606 or does so concurrently with the adoption of this guidance. The Company early adopted this guidance as of January 1, 2019, and implemented the new guidance in its consideration of the accounting for the DSE collaboration signed on January 2, 2019. Refer to Note 3 "Collaborations with Third Parties" and the Collaboration Revenue accounting policy above for further information. In February 2016, the FASB issued ASU 2016-02, which was amended by subsequent updates (collectively the “lease standard” or “ASC 842”), and is intended to improve financial reporting about leasing transactions. The updated guidance requires a lessee to recognize assets and liabilities for leases with lease terms of more than twelve months. The Company adopted the standard on January 1, 2019 using the modified retrospective method. Results for the reporting period beginning after December 31, 2018 have been presented in accordance with the standard, while results for prior periods have not been adjusted. The Company recognized $1.0 million and $1.0 million of operating lease assets and operating lease liabilities, respectively, on the Company’s balance sheets as of January 1, 2019, primarily related to the lease agreement for the Company’s principal executive office. Refer to Note 13 "Leases" for more information on the Company’s leases. In June 2016, the FASB issued ASU 2016-13 which requires financial instruments to be recognized at an estimate of current expected credit losses. As part of the ASU, financial assets measured at amortized cost will be presented at the net amount expected to be collected. In addition, companies will recognize an allowance for credit losses on available-for-sale investments rather than reducing the amortized cost in an other-than-temporary impairment. The standard is effective for public companies for fiscal years beginning after December 15, 2019, and interim periods within those years. The Company will adopt the standard effective January 1, 2020. The Company believes the adoption of this standard will have an immaterial impact on the Company’s accounting for its current financial instruments presented on the balance sheets at December 31, 2019; however, the Company will continue to evaluate the impact of this standard on its future financial instruments. In August 2018, the FASB issued ASU 2018-15 which includes provisions to clarify customer’s accounting for implementation costs incurred in a cloud computing arrangement. Under the updated guidance, a customer in a cloud computing arrangement that is a service contract should follow the internal-use software guidance to determine how to account for costs incurred in implementation. The updated guidance also requires certain classification on the balance sheets, statements of operations and statements of cash flows as well as additional quantitative and qualitative disclosures. The standard is effective for public companies for fiscal years beginning after December 15, 2019, and interim periods within those years. Entities can choose to adopt the new guidance prospectively or retrospectively. The ​ 2. Summary of Significant Accounting Policies (Continued) Company will adopt the standard effective January 1, 2020, and has chosen to adopt the standard prospectively. The Company does not believe the adoption of this standard to have a material impact to the Company’s balance sheets, statements of operations or statements of cash flows.

Collaborations with Third Parti

Collaborations with Third Parties	12 Months Ended
	Dec. 31, 2019
Collaborations with Third Parties
Collaborations with Third Parties	3. Collaborations with Third Parties Agreement Terms On January 2, 2019, the Company entered into a license and collaboration agreement with DSE. Pursuant to the agreement, the Company granted DSE exclusive commercialization rights to bempedoic acid and the bempedoic acid / ezetimibe combination tablet in the European Economic Area and Switzerland (“DSE Territory”). DSE will be responsible for commercialization in the DSE Territory. The Company remains responsible for clinical development, regulatory and manufacturing activities for the licensed products globally, including in the DSE Territory. Pursuant to the agreement, the consideration consists of a $150.0 million upfront cash payment as well as $150.0 million cash payment to the Company upon first commercial sales in the DSE Territory. The Company is also eligible to receive a substantial additional regulatory milestone payment upon the grant of the marketing authorisation in the European Union for the CV risk reduction label, depending on the range of relative risk reduction in the CLEAR Outcomes study. In addition, the Company is eligible to receive additional sales milestone payments related to total net sales achievements for DSE in the DSE Territory. Finally, the Company will receive tiered fifteen percent (15%) to twenty-five percent (25%) royalties on net DSE Territory sales. The agreement calls for both parties to participate in a Joint Collaboration Committee (the “JCC”). The JCC is comprised of executive management from each company and the Company will lead in all aspects related to development and DSE will lead in all aspects related to commercialization in the DSE Territory. Collaboration Revenue The Company considered the guidance under ASC 606 and concluded that the agreement was in the scope of ASC 606. The Company concluded that the upfront payment of $150.0 million should be included in the transaction price and related to the following performance obligations under the agreement: 1) the license to the Company’s intellectual property and 2) the obligation to provide ongoing regulatory and development activities. The Company used the adjusted market assessment approach in determining the standalone selling price of the Company’s intellectual property and the expected cost plus margin approach in determining the standalone selling price of the Company’s obligation to provide ongoing regulatory and development activities. Accordingly, during the year ended December 31, 2019, the Company recognized $148.4 million of collaboration revenue related to the $150.0 million upfront payment, respectively. The $148.4 million relates to the performance obligations for the license to the Company’s intellectual property and a portion of ongoing regulatory and development activities conducted during the period ended December 31, 2019, in the amounts of $144.4 million and $4.0 million, respectively. The remaining $1.6 million of the upfront payment was deferred as of December 31, 2019 due to an on-going performance obligation related to the ongoing regulatory efforts related to the MAA in the DSE Territory. This deferred revenue will be recognized ratably over the period leading up to the approval of the MAA acceptance by the EMA. All future potential milestone amounts were not included in the transaction price, as they were all determined to be fully constrained following the concepts of ASC 606 due to the fact that such amounts hinge on regulatory approval. Additionally, the Company expects that any consideration related to royalties and sales-based milestones will be recognized when the subsequent sales occur. The Company has not yet recognized any revenue for milestone payments as the related regulatory and commercial milestones have not yet been achieved. ​

Warrants

Warrants	12 Months Ended
	Dec. 31, 2019
Warrants
Warrants	4. Warrants In June 2014, the Company entered into a loan and security agreement (the "Credit Facility") with Oxford Finance LLC which provided for borrowings of $5.0 million under the term loan (the "Term A Loan"). On June 30, 2014, the Company received proceeds of $5.0 million from the issuance of secured promissory notes under the Term A Loan, which were collateralized by substantially all of the Company's personal property, other than its intellectual property. The Term A Loan was fully repaid in July 2018. In connection with the Credit Facility entered into in June 2014, the Company issued a warrant to purchase 8,230 shares of common stock at an exercise price of $15.19. The warrant was recorded at fair value of $0.1 million to additional-paid-in-capital in accordance with ASC 815-10 based upon the allocation of the debt proceeds. During the year ended December 31, 2019, 8,230 warrants were net exercised for 5,813 shares of the Company's common stock. During the year ended December 31, 2018, 177,123 warrants were net exercised for 159,944 shares of the Company's common stock and during the year ended December 31, 2017, 71,237 warrants were net exercised for 62,525 shares of the Company's common stock. As of December 31, 2019, the Company had no warrants outstanding.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies
Commitments and Contingencies	5. Commitments and Contingencies On June 26, 2019, the Company entered into a RIPA with Oberland. Pursuant to the RIPA, Oberland paid the Company $125.0 million at closing, less certain issuance costs, and, subject to the terms and conditions of the RIPA, the Company is eligible for an additional $25.0 million upon certain regulatory approval of the Company's product candidates and $50.0 million at its option upon reaching certain sales thresholds. As consideration for the payments, Oberland has the right to receive certain revenue interests from the Company based on the net sales of certain products, once approved, which will be tiered payments initially ranging from 2.5% to 7.5% of our net sales in the covered territory (as detailed in the RIPA). The initial mid-single digit repayment rate on U.S. revenue steps down to less than one percent rate upon certain revenue achievements. Esperion reacquires 100% revenue rights upon repayment completion. The Company recorded the proceeds from the RIPA as a liability on the balance sheets and are accounting for the RIPA under the effective-interest method over the estimated life of the RIPA. Future payments under the RIPA may range from $0.1 million in the next year to a maximum total payment of $243.8 million beyond one year. Per the terms of the agreement, every $100 million of net sales generated, less than or equal to $250 million in an annual aggregate, would result in a repayment obligation of approximately $7.5 million at the stated repayment rate in the first year. In the future, as net sales thresholds set forth in the agreement are met and the repayment percentage rate changes, the amount of the obligation and timing of payment is likely to change. As products are not yet approved for sale, the exact timing or amounts of repayment is likely to change each reporting period. A significant increase or decrease in net sales will materially impact the revenue interest liability, interest expense and the time period for repayment. Refer to Note 10 “Liability Related to the Revenue Interest Purchase Agreement” for further information. In February 2014, the Company entered into an operating lease agreement for its principal executive offices located in Ann Arbor, Michigan commencing in April 2014, with a term of 63 months . The Company’s lease provides for fixed monthly rent for the term of the lease, with monthly rent increasing every 12 months subsequent to the first three months of the lease, and also provides for certain rent adjustments to be paid as determined by the landlord. On July 6, 2018, the Company entered into the first amendment of the lease for the Company's principal executive office in Ann Arbor, Michigan. The amended lease is to increase the current 7,941 rentable square feet of office space by 11,471 rentable square feet, together with the right to use common areas and facilities in common with the landlord and other tenants. The term of the lease commences with respect to all of the space in the leased premises on the later to occur of (i) the date upon which landlord delivers the premises to the Company under the terms of the lease with the delivery conditions set forth in the lease satisfied and (ii) November 1, 2018 (the "Lease Commencement Date"). The term of the lease shall end 60 months after the Lease Commencement Date. Under the terms of the lease, following the first month (during which the base rent is $0 ) and the second month (during which the base rent is $15,990 ), the base rent, subject to certain adjustments, for the leased premises will start at approximately $19,412 per month, plus certain operating expenses and taxes, and shall increase on an annual basis and/or as otherwise provided in the lease agreement. In addition, the Company has also entered into various operating leases related to vehicle leases and other IT equipment. Refer to Note 13 "Leases" for further information. ​ 5. Commitments and Contingencies (Continued) The following table summarizes the Company’s estimated future minimum commitments as of December 31, 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Less than ​ ​ ​ ​ ​ ​ ​ More than ​ Total 1 Year 1 - 3 Years 3 - 5 Years 5 Years ​ ​ (in thousands) Revenue interest liability ​ $ 292,500 ​ $ — ​ $ — ​ $ — ​ $ 292,500 Operating leases ​ ​ 1,741 ​ ​ 538 ​ ​ 987 ​ ​ 216 ​ ​ — Total ​ $ 294,241 ​ $ 538 ​ $ 987 ​ $ 216 ​ $ 292,500 ​ Legal Proceedings On January 12, 2016, a purported stockholder of the Company filed a putative class action lawsuit in the United States District Court for the Eastern District of Michigan, against the Company and Tim Mayleben, captioned Kevin L. Dougherty v. Esperion Therapeutics, Inc., et al. On December 15, 2016, a purported stockholder of the Company filed a derivative lawsuit in the Court of Chancery of the State of Delaware against Tim Mayleben, Roger Newton, Mary McGowan, Nicole Vitullo, Dov Goldstein, Daniel Janney, Antonio Gotto Jr., Mark McGovern, Gilbert Omenn, Scott Braunstein, and Patrick Enright. The Company is named as a nominal defendant. The lawsuit alleges that the defendants breached their fiduciary duties to the Company when they made or approved improper statements on August 17, 2015, regarding the Company’s lead product candidate’s path to FDA approval, and failed to ensure that reliable systems of internal controls were in place at the Company. On February 8, 2019, the Company and defendants filed a motion to dismiss the derivative lawsuit. On April 23, 2019, the plaintiff filed an opposition to the motion to dismiss the derivative lawsuit, and the Company filed a reply brief on May 15, 2019. On November 6, 2019, the court held a hearing on the motion to dismiss. On February 13, 2020, the court granted the motion to dismiss with prejudice and entered judgment in the Company’s favor. On May 7, 2018, a purported stockholder of the Company filed a putative class action lawsuit in the United States District Court for the Eastern District of Michigan, captioned Kevin Bailey v. Esperion Therapeutics, Inc., et al. (No. 18-cv-11438 ​ 5. Commitments and Contingencies (Continued) dismiss the amended complaint, and that motion was fully briefed on December 18, 2018. The lawsuit sought, among other things, compensatory damages in connection with an allegedly inflated stock price between February 22, 2017, and May 22, 2018, as well as attorneys’ fees and costs. On February 19, 2019, the court granted the Company’s motion to dismiss with prejudice and entered judgment in the Company’s favor.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2019
Property and Equipment
Property and Equipment	6. Property and Equipment Property and equipment consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2018 ​ ​ (in thousands) Lab equipment ​ $ — ​ $ 232 Computer equipment ​ 256 ​ 51 Software ​ 615 ​ 205 Furniture, fixtures and other ​ 908 ​ 719 Leasehold improvements ​ 298 ​ 309 Assets in Progress ​ 99 ​ — Subtotal ​ 2,176 ​ 1,516 Less accumulated depreciation and amortization ​ 1,031 ​ 996 Property and equipment, net ​ $ 1,145 ​ $ 520 ​ Depreciation expense was $0.3 million, $0.3 million, and $0.3 million for the years ended December 31, 2019, 2018 and 2017, respectively.

Other Accrued Liabilities

Other Accrued Liabilities	12 Months Ended
	Dec. 31, 2019
Other Accrued Liabilities
Other Accrued Liabilities	7. Other Accrued Liabilities Other accrued liabilities consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2018 ​ ​ (in thousands) Accrued compensation ​ $ 7,818 ​ $ 1,833 Accrued professional fees ​ 3,842 ​ ​ 1,228 Accrued franchise and property taxes ​ 37 ​ 44 Accrued other ​ 174 ​ 296 Total other accrued liabilities ​ $ 11,871 ​ $ 3,401 ​

Investments

Investments	12 Months Ended
	Dec. 31, 2019
Investments
Investments	8. Investments The following table summarizes the Company’s cash equivalents and investments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 20,970 ​ $ — ​ $ — ​ $ 20,970 U.S. treasury notes ​ ​ 2,497 ​ ​ — ​ ​ — ​ ​ 2,497 Commercial paper ​ ​ 4,494 ​ ​ — ​ ​ — ​ ​ 4,494 Short-term investments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Certificates of deposit ​ ​ 245 ​ ​ — ​ ​ — ​ ​ 245 U.S. treasury notes ​ 29,155 ​ 23 ​ — ​ 29,178 Commercial paper ​ 5,228 ​ — ​ — ​ 5,228 Total ​ $ 62,589 ​ $ 23 ​ $ — ​ $ 62,612 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2018 ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 34,526 ​ $ — ​ $ — ​ $ 34,526 Short-term investments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Certificates of deposit ​ ​ 3,873 ​ ​ — ​ ​ (7) ​ ​ 3,866 U.S. treasury notes ​ 44,897 ​ — ​ (142) ​ 44,755 U.S. government agency securities ​ 50,598 ​ — ​ (169) ​ 50,429 Long-term investments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Certificates of deposit ​ 244 ​ — ​ (1) ​ 243 Total ​ $ 134,138 ​ $ — ​ $ (319) ​ $ 133,819 ​ At December 31, 2019, remaining contractual maturities of available-for-sale investments classified as current on the balance sheet were less than 12 months, and remaining contractual maturities of available-for-sale investments classified as long-term were less than two years. The company does not intend to sell the investments before maturity. During the years ended December 31, 2019, 2018 and 2017, other income, net in the statements of operations includes interest income on available-for-sale investments of $3.7 million, $2.6 million and $2.5 million, respectively. Other income, net in the statements of operations includes income for the accretion of premiums and discounts on investments of $0.3 million and $0.2 million during the years ended December 31, 2019 and 2018, respectively, and expense for the amortization of premiums and discounts on investments of $0.3 million during the year ended December 31, 2017. There were no unrealized gains or losses on investments reclassified from accumulated other comprehensive loss to other income, net in the statements of operations during the year ended December 31, 2019.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Measurements
Fair Value Measurements	9. Fair Value Measurements The Company follows accounting guidance that emphasizes that fair value is a market-based measurement, not an entity-specific measurement. Fair value is defined as “the price that would be received to sell an asset or paid to transfer ​ 9. Fair Value Measurements (Continued) a liability in an orderly transaction between market participants at the measurement date.” Fair value measurements are defined on a three level hierarchy: Level 1 inputs: Quoted prices for identical assets or liabilities in active markets; ​ ​ ​ Level 2 inputs: ​ Observable inputs other than Level 1 prices, such as quoted market prices for similar assets or liabilities or other inputs that are observable or can be corroborated by market data; and ​ ​ ​ Level 3 inputs: ​ Unobservable inputs that are supported by little or no market activity and require the reporting entity to develop assumptions that market participants would use when pricing the asset or liability. ​ The following table presents the Company’s financial assets and liabilities that have been measured at fair value on a recurring basis: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Description Total Level 1 Level 2 Level 3 ​ ​ (in thousands) December 31, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 20,970 ​ $ 20,970 ​ $ — ​ $ — Investments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Certificates of deposit ​ 245 ​ 245 ​ — ​ — U.S. treasury notes ​ 31,675 ​ 31,675 ​ — ​ — Commercial paper ​ 9,722 ​ — ​ 9,722 ​ — Total assets at fair value ​ $ 62,612 ​ $ 52,890 ​ $ 9,722 ​ $ — December 31, 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 34,526 ​ $ 34,526 ​ $ — ​ $ — Investments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Certificates of deposit ​ 4,109 ​ 4,109 ​ — ​ — U.S. treasury notes ​ 44,755 ​ 44,755 ​ — ​ — U.S. government agency securities ​ 50,429 ​ — ​ 50,429 ​ — Total assets at fair value ​ $ 133,819 ​ $ 83,390 ​ $ 50,429 ​ $ — ​ At December 31, 2019, the fair value of the $132.5 million revenue interest liability is based on the Company’s contractual repayment obligation to Eiger III SA LLC (“Oberland”), an affiliate of Oberland Capital LLC, based on the current estimates of future revenues, over the life of the Revenue Interest Purchase Agreement (“RIPA”). The liability is considered a Level 3 input based on the three level hierarchy. Refer to Note 10 “Liability Related to the Revenue Interest Purchase Agreement” for further information. There were no transfers between Levels 1 , 2 or 3 during the years ended December 31, 2019 or December 31, 2018.

Liability Related to the Revenu

Liability Related to the Revenue Interest Purchase Agreement	12 Months Ended
	Dec. 31, 2019
Liability Related to the Revenue Interest Purchase Agreement
Liability Related to the Revenue Interest Purchase Agreement	10. Liability Related to the Revenue Interest Purchase Agreement On June 26, 2019, the Company entered into a RIPA with Oberland, as agent for purchasers party thereto (the “Purchasers”), and the Purchasers named therein, to obtain financing in respect to the commercialization and further development of bempedoic acid and the bempedoic acid / ezetimibe combination tablet and other working capital needs. Pursuant to the RIPA, the Company received $125.0 million at closing, less certain issuance costs. The Company will also be entitled to receive up to approximately $75.0 million in subsequent installments subject to the terms and conditions set forth in the RIPA: (i) $25.0 million upon certain regulatory approval of its product candidates and (ii) $50.0 million, at the Company’s option, upon reaching $100.0 million trailing worldwide six-month net sales any time prior to December 31, 2021 (the “Third Payment”). 10. Liability Related to the Revenue Interest Purchase Agreement (Continued) As consideration for such payments, the Purchasers will have a right to receive certain revenue interests (the “Revenue Interests”) from the Company based upon net sales of the Company’s certain products, once approved, which will be tiered payments initially ranging from 2.5% to 7.5% of the Company’s net sales in the covered territory (the “Covered Territory”); provided that (a) if annual net sales equal or exceed $350.0 million by December 31, 2021 (the “Sales Threshold”), the initially tiered revenue interest rate will be decreased to a single rate of 2.5% of the Company’s net sales in the Covered Territory, beginning on January 1, 2022, and (b) if annual net sales equal or exceed the Sales Threshold and if the Purchasers receive 100% of their invested capital by December 31, 2024, the revenue interest rate will be decreased to a single rate of 0.4% of the Company’s net sales in the Covered Territory beginning on January 1, 2025. If the Third Payment is drawn down by the Company, the applicable royalty rates will increase by one -third. The Covered Territory is the United States, but is subject to expand to include the world-wide net sales if the Company’s annual U.S. net sales are less than $350.0 million for the year ended December 31, 2021. The U.S. net sales milestone thresholds are not to be taken as financial guidance. The Purchasers’ rights to receive the Revenue Interests shall terminate on the date on which the Purchasers have received Revenue Interests payments of 195% of the then aggregate purchase price (the “Cumulative Purchaser Payments”) paid to the Company, unless the RIPA is terminated earlier. Under the RIPA, the Company has an option (the “Call Option”) to terminate the RIPA and repurchase future Revenue Interests at any time upon advance written notice. Additionally, the Purchasers have an option (the “Put Option”) to terminate the RIPA and to require the Company to repurchase future Revenue Interests upon enumerated events such as a bankruptcy event, an uncured material breach, a material adverse effect or a change of control. If the Put Option is exercised prior to the first anniversary of the closing date by the Purchasers (except pursuant to a change of control), the required repurchase price will be 120% of the Cumulative Purchaser Payments (minus all payments Company has made to the Purchasers in connection with the Revenue Interests). In all other cases, if the Put Option or the Call Option are exercised, the required repurchase price will be 175% of the Cumulative Purchaser Payments (minus all payments Company has made to the Purchasers in connection with the Revenue Interests), if such option is exercised prior to the third anniversary of the closing date, and 195% of the Cumulative Purchaser Payments (minus all payments Company has made to the Purchasers in connection with the Revenue Interests), if such option is exercised thereafter. In addition, the RIPA contains various representations and warranties, information rights, non-financial covenants, indemnification obligations and other provisions that are customary for a transaction of this nature. In connection with the arrangement, as of December 31, 2019, the Company has recorded a liability, referred to as the “Revenue interest liability” on the balance sheets, of $132.5 million, net of $0.6 million of capitalized issuance costs in connection with the RIPA. The Company imputes interest expense associated with this liability using the effective interest rate method. The effective interest rate is calculated based on the rate that would enable the debt to be repaid in full over the anticipated life of the arrangement. The interest rate on this liability may vary during the term of the agreement depending on a number of factors, including the level of forecasted net sales. The Company evaluates the interest rate quarterly based on its current net sales forecasts utilizing the prospective method. A significant increase or decrease in net sales will materially impact the revenue interest liability, interest expense and the time period for repayment. The Company recorded approximately $8.1 million in interest expense related to this arrangement for the year ended December 31, 2019. We received $125.0 million in exchange for entering into the RIPA, with an effective annual imputed interest rate of 12.6%. The Company incurred $0.6 million of issuance costs in connection with the RIPA, which will be amortized to interest expense over the estimated term of the RIPA. Payments made to Oberland as a result of the Company’s net sales will reduce the revenue interest liability. ​ 10. Liability Related to the Revenue Interest Purchase Agreement (Continued) The following table summarizes the revenue interest liability activity during the year ended December 31, 2019: ​ ​ ​ ​ ​ (in thousands) Revenue interest liability at June 26, 2019 ​ $ 125,000 Interest expense recognized ​ 8,120 Capitalized issuance costs ​ (576) Revenue interest liability at December 31, 2019 ​ $ 132,544 ​

Stock Compensation

Stock Compensation	12 Months Ended
	Dec. 31, 2019
Stock Compensation
Stock Compensation	11. Stock Compensation 2017 Inducement Equity Plan In May 2017, the Company's board of directors approved the 2017 Inducement Equity Plan (the "2017 Plan"). The number of shares of common stock available for awards under the 2017 Plan was set to 750,000, with any shares of common stock that are forfeited, cancelled, held back upon the exercise or settlement of an award to cover the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of common stock, or otherwise terminated (other than by exercise) under the 2017 Plan added back to the shares of common stock available for issuance under the 2017 Plan. The 2017 Plan provides for the granting of stock options, stock appreciation rights, restricted stock awards, restricted stock units ("RSUs"), unrestricted stock awards and dividend equivalent rights. In November 2019, the Company's board of directors approved an amendment to the 2017 Plan to increase the number of shares of common stock available for issuance under the 2017 Plan by 400,000 shares. 2013 Stock Option and Incentive Plan In May 2015, the Company’s stockholders approved the amended and restated 2013 Stock Option and Incentive Plan (as amended, the “2013 Plan”) which, among other things, increased the number of shares of common stock reserved for issuance thereunder. The number of shares of common stock available for awards under the 2013 Plan was increased by 923,622 shares from 2,051,378 shares to 2,975,000 shares, plus (i) shares of common stock that are forfeited, cancelled, held back upon the exercise or settlement of an award to cover the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of common stock or otherwise terminated (other than by exercise) under the 2013 Plan and the Company’s 2008 Incentive Stock Option and Restricted Stock Plan are added back to the shares of common stock available for issuance under the 2013 Plan, and (ii) on January 1, 2016, and each January 1, thereafter, the number of shares of common stock reserved and available for issuance under the 2013 Plan will be cumulatively increased by 2.5% of the number of shares of common stock outstanding on the immediately preceding December 31, or such lesser number of shares of common stock determined by the compensation committee. The 2013 Plan provides for the granting of stock options, stock appreciation rights, restricted stock awards, RSUs, unrestricted stock awards, cash-based awards, performance share awards and dividend equivalent rights. 2008 Stock Option and Restricted Stock Plan In April 2008, the Company adopted the 2008 Plan, administered by the Board of Directors or a committee appointed by the Board of Directors. The 2008 Plan provides for the granting of stock options and restricted stock to employees and nonemployees of the Company. Options granted under the 2008 Plan may either be incentive stock options, restricted stock awards or nonqualified stock options. Stock options and restricted stock grants may be granted to employees, directors and consultants. Stock awards under the 2008 Plan may be granted for up to ten years from the adoption of the 2008 Plan at prices no less than 100 percent of the fair value of the shares on the date of the grant as determined by (i) the closing price of the Company’s common stock on any national exchange, (ii) the National Association of Securities Dealers Inc. Automated Quotation System (“NASDAQ”), if so authorized for quotation as a NASDAQ security, or (iii) by reasonable application of a reasonable valuation method. The valuation methods utilized by the Company are consistent with the AICPA Technical Practice Aid. ​ 11. Stock Compensation (Continued) The Company incurs stock-based compensation expense related to stock options and RSUs. The fair value of RSUs is determined by the closing market price of the Company’s common stock on the date of grant. The fair value of stock options is calculated using a Black-Scholes option-pricing model. The Company accounts for stock-based compensation in accordance with the provisions of ASC 718, Compensation-Stock Compensation. Accordingly, compensation costs related to equity instruments granted are recognized over the requisite service periods of the awards on a straight-line basis at the grant-date fair value. In accordance with the adoption of ASU 2016-09, effective January 1, 2017, the Company accounts for forfeitures as they occur. Under the 2017 Plan, 2013 Plan and the 2008 Plan the vesting of options granted or restricted awards given will be determined individually with each option grant. Generally, 25 percent of the granted amount will vest upon the first anniversary of the option grant with the remainder vesting ratably on the first day of each calendar quarter for the following three years . Stock options have a 10 -year life and expire if not exercised within that period, or if not exercised within 90 days of cessation of providing service to the Company. The following table summarizes the activity relating to the Company’s options to purchase common stock for the year ended December 31, 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ Remaining ​ ​ ​ ​ ​ Number of ​ Exercise Price ​ Contractual ​ Aggregate ​ Options Per Share Term (Years) Intrinsic Value ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) Outstanding at December 31, 2018 5,303,723 ​ $ 37.01 7.42 ​ $ 83,473 Granted 542,875 ​ $ 46.95 ​ ​ ​ ​ ​ Forfeited or cancelled (vested and unvested) (519,140) ​ $ 50.24 ​ ​ ​ ​ ​ Exercised (649,529) ​ $ 18.12 ​ ​ ​ ​ ​ Outstanding at December 31, 2019 4,677,929 ​ $ 39.31 6.82 ​ $ 109,054 ​ The following table summarizes information about the Company’s stock option plan as of December 31, 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ Remaining ​ ​ ​ ​ ​ Number of ​ Exercise Price ​ Contractual ​ Aggregate ​ Options Per Share Term (Years) Intrinsic Value ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) Vested and expected to vest at December 31, 2019 4,677,929 ​ $ 39.31 6.82 ​ $ 109,054 Exercisable at December 31, 2019 2,993,362 ​ $ 34.24 5.84 ​ $ 86,698 ​ The total intrinsic value of stock options exercised during the years ended December 31, 2019, 2018 and 2017, was $17.7 million, $12.1 million and $4.0 million, respectively. The following table shows the weighted-average assumptions used to compute the stock-based compensation costs for the stock options granted to employees during each of the three years ending December 31, 2019, using the Black-Scholes option-pricing model: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended ​ ​ December 31, ​ 2019 2018 2017 Risk-free interest rate 2.10 % 2.75 % 2.04 % Dividend yield — ​ — ​ — ​ Weighted-average expected life of options (years) 6.25 ​ 6.21 ​ 6.19 ​ Volatility 73 % 72 % 73 % ​ ​ 11. Stock Compensation (Continued) The risk-free interest rate assumption was based on the United States Treasury’s rates for U.S. Treasury zero-coupon bonds with maturities similar to those of the expected term of the award being valued. The assumed dividend yield was based on the Company’s expectation of not paying dividends in the foreseeable future. The weighted-average expected life of the options was calculated using the simplified method as prescribed by the Securities and Exchange Commission Staff Accounting Bulletin No. 107 (“SAB No. 107”). This decision was based on the lack of relevant historical data due to the Company’s limited historical experience. In addition, due to the Company’s limited historical and predictive data, the estimated volatility incorporates the historical volatility of comparable companies whose share prices are publicly available. The weighted-average grant-date fair values of stock options granted during the years ended December 31, 2019, 2018 and 2017, were $31.18, $37.56, and $15.99, respectively. During the years ended December 31, 2019, 2018 and 2017, the Company recognized stock-based compensation expense related to stock options of $23.5 million, $23.4 million and $18.2 million, respectively. As of December 31, 2019, there was approximately $48.6 million of unrecognized compensation cost related to unvested options, which will be recognized over a weighted-average period of approximately 2.6 years. The following table summarizes the activity relating to the Company’s RSUs for the year ended December 31, 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Weighted-Average ​ RSUs Fair Value Per Share ​ ​ ​ ​ ​ ​ Outstanding and unvested at December 31, 2018 37,475 ​ $ 66.96 Granted 230,284 ​ $ 42.21 Forfeited or expired (4,083) ​ $ 36.73 Vested (17,710) ​ $ 64.71 Outstanding and unvested at December 31, 2019 245,966 ​ $ 44.45 ​ During the years ended December 31, 2019, 2018 and 2017, the Company recognized approximately $2.4 million, $0.6 million and $0.4 million, respectively, of stock-based compensation expense recognized related to RSUs. As of December 31, 2019, there was approximately $9.2 million of unrecognized stock-based compensation expense related to unvested RSUs, which will be recognized over a weighted-average period of approximately 3.1 years.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2019
Employee Benefit Plan
Employee Benefit Plan	12. Employee Benefit Plan During 2008, the Company adopted the Esperion Therapeutics, Inc. 401(k) Plan (the “401(k) Plan”), which qualifies as a deferred salary arrangement under Section 401(k) of the Internal Revenue Code. Under the 401(k) Plan, participating employees may defer a portion of their pretax earnings. The Company may, at its sole discretion, contribute for the benefit of eligible employees. Company contributions to the 401(k) Plan during the years ended December 31, 2019, 2018 and 2017, were $0.7 million, $0.3 million and $0.3 million, respectively.

Leases

Leases	12 Months Ended
	Dec. 31, 2019
Leases
Leases	13. Leases The Company has operating leases primarily related to the Company's principal executive office, automobile leases and other IT related equipment. The lease for the principal executive office has a lease term of 5 years and the automobile leases and IT equipment leases primarily have a term of 3 years . During the year ended December 31, 2019, the Company recognized $0.3 million of operating lease costs, recognized on the statements of operations, and paid cash for the amounts included in the measurement of lease liabilities of $0.3 million which were included in operating cash flows on the statements of cash flows. At December 31, 2019, the weighted-average remaining lease term of operating leases was 3.3 years and the weighted average discount rate was 6.5% . There were no right-of-use assets obtained in ​ 13. Leases (Continued) exchange for lease obligations in the twelve months ended December 31, 2019. The Company had no additional operating and finance leases that have not yet commenced as of December 31, 2019. The total rent expense for the years ended December 31, 2018 and 2017, recognized prior to the adoption of ASU 2016-02, was approximately $0.3 million, and $0.2 million, respectively. The following table summarizes the Company's future maturities of operating lease liabilities as of December 31, 2019: ​ ​ ​ ​ ​ (in thousands) 2020 ​ $ 538 2021 ​ 517 2022 ​ 470 2023 ​ 216 Total lease payments ​ 1,741 Less imputed interest ​ 178 Total ​ $ 1,563 ​ The following table summarizes supplemental balance sheet information related to leases as of December 31, 2019: ​ ​ ​ ​ Operating Leases (in thousands) Right of use operating lease assets (long-term) ​ 1,532 Total right of use operating lease assets ​ $ 1,532 ​ ​ ​ ​ Operating lease liabilities (short-term) ​ $ 454 Operating lease liabilities (long-term) ​ 1,109 Total lease obligations under operating leases ​ $ 1,563 ​

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Taxes
Income Taxes	14. Income Taxes There was no provision for income taxes for the years ended December 31, 2019, 2018 and 2017, because the Company has incurred operating losses since inception. At December 31, 2019, the Company concluded that it is not more likely than not that the Company will realize the benefit of its deferred tax assets due to its history of losses. Accordingly, a full valuation allowance has been applied against the net deferred tax assets. On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (“TCJA”) was signed into law making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 34% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S. Tax from a worldwide to a territorial system, and potential additional limitations on deductions related to interest expense and executive compensation. The Company recorded a reduction to its gross deferred tax assets of $50.4 million in 2017, the period in which the legislation was enacted. The reduction in the Company’s gross deferred tax assets was fully offset by an equal reduction in the Company’s valuation allowance, resulting in no additional net income tax expense from the tax law change. As of December 31, 2019, 2018 and 2017, the Company had deferred tax assets, before valuation allowance, of approximately $174.2 million, $152.2 million and $99.8 million, respectively. Realization of the deferred assets is dependent upon future taxable income, if any, the amount and timing of which are uncertain. Accordingly, the net deferred tax assets have been fully offset by a valuation allowance. As of December 31, 2019, 2018 and 2017, the Company had federal net operating loss (“NOL”) carryforwards of approximately $618.1 million, $539.2 million and $347.4 million, respectively. The federal NOL carryforwards will expire at various dates beginning in 2028, if not utilized. The Company filed certain amended state tax returns for tax years 2012-2015 during 2017 that resulted in ​ 14. Income Taxes (Continued) increasing the Company’s state NOL carryforward. As of December 31, 2019, 2018 and 2017, the Company had state NOL carryforwards of approximately $527.1 million, $526.6 million and $327.8 million, respectively. The state NOL carryforwards will expire at various dates beginning in 2022, if not utilized. A reconciliation of the U.S. statutory income tax rate to the Company’s effective tax rate is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2018 2017 Federal income tax (benefit) at statutory rate (21.0) % (21.0) % (34.0) % Change in tax rate (0.2) % 0.0 % 29.6 % Permanent items (1.0) % (0.5) % 0.1 % Other 0.7 % 0.5 % (0.9) % Amended Tax Returns ​ 0.0 % 0.0 % (4.5) % Change in valuation allowance 21.5 % 21.0 % 9.7 % Effective income tax rate 0.0 % 0.0 % 0.0 % ​ If the Company experiences a greater than 50 percentage point aggregate change in ownership of certain significant stockholders over a three-year period, a Section 382 ownership change could be deemed to have occurred. If a Section 382 change occurs, the Company’s future utilization of the net operating loss carryforwards and credits as of the ownership change will be subject to an annual limitation under Section 382 of the Internal Revenue Code of 1986, as amended, and similar state provisions. Such an annual limitation may result in the expiration of net operating losses before utilization. The Company’s reserves related to taxes are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. The Company recognized no material adjustment for unrecognized income tax benefits. Through December 31, 2019, the Company had no unrecognized tax benefits or related interest and penalties accrued. Significant components of the Company’s deferred tax assets are summarized in the table below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2018 ​ ​ ​ (in thousands) Deferred tax assets: ​ ​ ​ ​ ​ ​ Federal and state operating loss carryforwards ​ $ 154,912 ​ $ 138,299 Equity compensation ​ ​ 17,217 ​ ​ 13,542 Temporary differences ​ 2,089 ​ 341 Total deferred tax assets ​ 174,218 ​ 152,182 Valuation allowance ​ (174,218) ​ (152,182) Net deferred tax assets ​ $ — ​ $ — ​

Net Loss Per Common Share

Net Loss Per Common Share	12 Months Ended
	Dec. 31, 2019
Net Loss Per Common Share
Net Loss Per Common Share	15. Net Loss Per Common Share Basic net loss per share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is computed by dividing net loss by the weighted-average number of common stock equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, warrants for common stock, stock options and unvested restricted stock and RSUs are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. ​ 15. Net Loss Per Common Share (Continued) The shares outstanding at the end of the respective periods presented below were excluded from the calculation of diluted net loss per share due to their anti-dilutive effect: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ December 31, ​ 2019 2018 2017 Warrants for common stock — 8,230 ​ 185,353 Common shares under option 4,677,929 5,303,723 ​ 4,159,151 Unvested RSUs 245,966 37,475 ​ 10,003 Total potential dilutive shares 4,923,895 5,349,428 ​ 4,354,507 ​

Statements of Cash Flows_2

Statements of Cash Flows	12 Months Ended
	Dec. 31, 2019
Statements of Cash Flows.
Statements of Cash Flows	16. Statements of Cash Flows The following table provides a reconciliation of cash and cash equivalents and restricted cash presented on the balance sheets to the same amounts presented on the statements of cash flows on December 31, 2019 and 2018. ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ ​ 2019 ​ 2018 Cash and cash equivalents ​ $ 166,130 ​ $ 36,973 Restricted cash ​ 928 ​ — Total cash, cash equivalents and restricted cash shown on the statements of cash flows ​ $ 167,058 ​ $ 36,973 ​

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2019
Selected Quarterly Financial Data (Unaudited)
Selected Quarterly Financial Data (Unaudited)	17. Selected Quarterly Financial Data (Unaudited) The following table summarizes the unaudited quarterly financial data for the last two years: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ March 31 June 30 September 30 December 31 ​ ​ ​ (in thousands, except share and per share data) Revenues: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Collaboration revenue ​ $ 145,419 ​ $ 982 ​ $ 981 ​ $ 982 Total Revenues ​ 145,419 ​ 982 ​ 981 ​ 982 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating expenses: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Research and development ​ $ 46,308 ​ $ 42,788 ​ $ 48,281 ​ $ 38,234 General and administrative ​ 12,182 ​ 13,492 ​ 18,468 ​ 21,712 Total operating expenses ​ 58,490 ​ 56,280 ​ 66,749 ​ 59,946 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gain (loss) from operations: ​ 86,929 ​ (55,298) ​ (65,768) ​ (58,964) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest expense ​ — ​ — ​ (3,996) ​ (4,124) Other income, net ​ 450 ​ 1,077 ​ 1,387 ​ 1,142 Net gain (loss) ​ $ 87,379 ​ $ (54,221) ​ $ (68,377) ​ $ (61,946) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net gain (loss) per common share – basic (1) ​ $ 3.26 ​ $ (2.01) ​ $ (2.52) ​ $ (2.26) Net gain (loss) per common share – diluted ​ $ 3.07 ​ $ (2.01) ​ $ (2.52) ​ $ (2.26) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average shares outstanding - basic ​ ​ 26,842,785 ​ ​ 26,968,818 ​ ​ 27,171,769 ​ ​ 27,371,067 Weighted-average shares outstanding - diluted ​ 28,449,767 ​ 26,968,818 ​ 27,171,769 ​ 27,371,067 ​ ​ 17. Selected Quarterly Financial Data (Unaudited) (Continued) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2018 ​ March 31 June 30 September 30 December 31 ​ ​ (in thousands, except share and per share data) Operating expenses: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Research and development ​ $ 40,940 ​ $ 39,524 ​ $ 41,551 ​ $ 49,473 General and administrative ​ 5,954 ​ 6,956 ​ 9,011 ​ 11,176 Total operating expenses ​ 46,894 ​ 46,480 ​ 50,562 ​ 60,649 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Loss from operations: ​ (46,894) ​ (46,480) ​ (50,562) ​ (60,649) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other income, net ​ 764 ​ 750 ​ 651 ​ 610 Net loss ​ $ (46,130) ​ $ (45,730) ​ $ (49,911) ​ $ (60,039) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss per common share - basic and diluted ​ $ (1.73) ​ $ (1.71) ​ $ (1.86) ​ $ (2.24) Weighted-average shares outstanding - basic and diluted ​ 26,605,189 ​ 26,786,796 ​ 26,804,026 ​ 26,818,331 (1) Due to the use of weighted average shares outstanding for each quarter for calculating net loss per common share, the sum of the quarterly net loss per common share amounts may not equal the net loss per common share amount for the full year.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Summary of Significant Accounting Policies
Use of Estimates	Use of Estimates The preparation of financial statements in accordance with generally accepted accounting principles in the United States requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, expenses and related disclosures. Actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company invests its excess cash in bank deposits, money market accounts, and short-term investments. The Company considers all highly liquid investments with an original maturity of 90 days or less at the time of purchase to be cash equivalents. Cash equivalents are reported at fair value.
Restricted Cash	Restricted Cash Restricted cash consists of legally restricted amounts held by financial institutions pursuant to contractual arrangements.
Investments	Investments Investments are considered to be available-for-sale and are carried at fair value. Unrealized gains and losses, if any, are reported as a separate component of stockholders’ equity. The cost of investments classified as available-for-sale are adjusted for the amortization of premiums and accretion of discounts to maturity and recorded in other income, net. Realized gains and losses, if any, are determined using the specific identification method and recorded in other income, net. Investments with original maturities beyond 90 days at the date of purchase and which mature at, or less than twelve months from, the balance sheet date are classified as current. Investments with a maturity beyond twelve months from the balance sheet date are classified as long-term.
Concentration of Credit Risk	Concentration of Credit Risk Cash, cash equivalents, and marketable securities consist of financial instruments that potentially subject the Company to concentrations of credit risk. The Company has established guidelines for investment of its excess cash and believes the guidelines maintain safety and liquidity through diversification of counterparties and maturities.
Segment Information	Segment Information The Company views its operations and manages its business in one operating segment, which is the business of researching, developing and commercializing therapies for the treatment of patients with elevated LDL-C. ​ 2. Summary of Significant Accounting Policies (Continued)
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company’s cash, cash equivalents, restricted cash and investments are carried at fair value. Financial instruments, including other prepaid and current assets, accounts payable and accrued liabilities are carried at cost, which approximates fair value. Debt is carried at amortized cost, which approximates fair value.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are recorded at cost, less accumulated depreciation. Depreciation is provided using the straight-line method over the estimated useful lives of the respective assets, generally three to ten years . Leasehold improvements are amortized over the lesser of the lease term or the estimated useful lives of the related assets.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. The impairment loss, if recognized, would be based on the excess of the carrying value of the impaired asset over its respective fair value. No impairment losses have been recorded through December 31, 2019.
Leases	Leases The Company reviews all arrangements to determine if the contract contains a lease or an embedded lease using the criteria in Accounting Standards Codification ("ASC") 842. If a lease is identified, the Company reviews the consideration in the contract and separates the lease components from the nonlease components. In addition, the Company reviews the classification of the lease between operating and finance leases. According to ASC 842, lessees should discount lease payments at the lease commencement date using the rate implicit in the lease. If the rate implicit in the lease is not readily determinable, a lessee must use its incremental borrowing rate for purposes of classifying the lease and measuring the right-of-use asset and liability. To the extent the rate is not implicit in the lease, the Company uses the incremental borrowing rate it would have to pay to borrow on a collateralized basis over a similar term in an amount equal to the lease payments in a similar economic environment.
Revenue Interest Liability	Revenue Interest Liability The revenue interest liability is presented net of deferred issuance costs on the balance sheets. The Company imputes interest expense associated with this liability using the effective interest rate method. The effective interest rate is calculated based on the rate that would enable the debt to be repaid in full over the anticipated life of the arrangement. The interest rate on the liability may vary during the term of the agreement depending on a number of factors, including the level of forecasted net sales. The Company evaluates the interest rate quarterly based on its current net sales forecasts utilizing the prospective method.
Revenue Recognition	Revenue Recognition a. Collaboration Revenue The Company has entered into an agreement related to its activities to develop, manufacture, and commercialize its product candidates. The Company earns collaboration revenue in connection with a collaboration agreement to develop and/or commercialize product candidates where the Company deems the collaborator to be the customer. The Company has adopted ASC 606, Revenue from Contracts with Customers, and under the terms of the standard, revenue is measured as the amount of consideration expected to be entitled to in exchange for transferring promised goods or providing services to a customer. Revenue is recognized when (or as) the Company satisfies performance obligations ​ 2. Summary of Significant Accounting Policies (Continued) under the terms of a contract. Depending on the terms of the arrangement, the Company may defer the recognition of all or a portion of the consideration received as the performance obligations are satisfied. The collaboration agreement may require the Company to deliver various rights, services, and/or goods across the entire life cycle of a product or product candidate. In the agreement involving multiple goods or services promised to be transferred to a customer, the Company must assess, at the inception of the contract, whether each promise represents a separate performance obligation (i.e., is "distinct"), or whether such promises should be combined as a single performance obligation. The terms of the agreement typically include consideration to be provided to the Company in the form of non-refundable up-front payments, development milestones, sales milestones, and royalties on sales of products within a respective territory. At the inception of the contract, the transaction price reflects the amount of consideration the Company expects to be entitled to in exchange for transferring promised goods or services to its customer. In the arrangement where the Company satisfies performance obligation(s) during the regulatory phase over time, the Company recognizes collaboration revenue typically using an input method on the basis of regulatory costs incurred relative to the total expected cost which determines the extent of progress toward completion. The Company reviews the estimate of the transaction price and the total expected cost each period, and makes revisions to such estimates as necessary. Under the Company's collaboration agreement, product sales and cost of sales may be recorded by the Company's collaborators as they are deemed to be the principal in the transaction. The Company receives royalties from the commercialization of such products, and records its share of the variable consideration, representing a percentage of net product sales, as collaboration revenue in the period in which such underlying sales occur and costs are incurred by the collaborator. The collaborator will provide the Company with estimates of its royalties for such quarter; these estimates are reconciled to actual results in the subsequent quarter, and the royalty is adjusted accordingly, as necessary. Please refer to the discussion in Note 3 "Collaborations with Third Parties" for further discussion of the accounting related to the collaboration agreement.
Research and Development	Research and Development Research and development expenses consist of costs incurred to further the Company’s research and development activities and include salaries and related benefits, costs associated with clinical activities, nonclinical activities, regulatory activities, manufacturing activities to support clinical activities and commercial product manufacturing supply as the Company approaches anticipated approval, research-related overhead expenses and fees paid to external service providers that conduct certain research and development, clinical, and manufacturing activities on behalf of the Company. Research and development costs are expensed as incurred.
Accrued Clinical Development Costs	Accrued Clinical Development Costs Outside research costs are a component of research and development expense. These expenses include fees paid to clinical research organizations and other service providers that conduct certain clinical and product development activities on behalf of the Company. Depending upon the timing of payments to the service providers, the Company recognizes prepaid expenses or accrued expenses related to these costs. These accrued or prepaid expenses are based on management’s estimates of the work performed under service agreements, milestones achieved and experience with similar contracts. The Company monitors each of these factors and adjusts estimates accordingly.
Income Taxes	Income Taxes The Company utilizes the liability method of accounting for income taxes as required by ASC 740, Income Taxes. Under this method, deferred tax assets and liabilities are determined based on differences between financial reporting ​ 2. Summary of Significant Accounting Policies (Continued) and the tax basis of assets and liabilities and are measured using enacted tax rates and laws that will be in effect when the differences are expected to reverse. The Company has incurred annual operating losses since inception. Accordingly, it is not more likely than not that the Company will realize a tax benefit from its deferred tax assets and as such, it has recorded a full valuation allowance.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based compensation in accordance with the provisions of ASC 718, Compensation—Stock Compensation. Accordingly, compensation costs related to equity instruments granted are recognized over the requisite service periods of the awards on a straight-line basis at the grant-date fair value calculated using a Black-Scholes option-pricing model. The Company accounts for forfeitures as they occur. Expense is recognized during the period the related services are rendered.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In November 2018, the Financial Accounting Standards Board ("FASB") issued Accounting Standard Update ("ASU") 2018-08, which clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606 when the collaborative arrangement participant is a customer in the context of a unit of account. The standard is effective for public companies for fiscal years beginning after December 15, 2019, and interim periods within those years. Early adoption is permitted, included in any interim period, provided an entity has already adopted ASC 606 or does so concurrently with the adoption of this guidance. The Company early adopted this guidance as of January 1, 2019, and implemented the new guidance in its consideration of the accounting for the DSE collaboration signed on January 2, 2019. Refer to Note 3 "Collaborations with Third Parties" and the Collaboration Revenue accounting policy above for further information. In February 2016, the FASB issued ASU 2016-02, which was amended by subsequent updates (collectively the “lease standard” or “ASC 842”), and is intended to improve financial reporting about leasing transactions. The updated guidance requires a lessee to recognize assets and liabilities for leases with lease terms of more than twelve months. The Company adopted the standard on January 1, 2019 using the modified retrospective method. Results for the reporting period beginning after December 31, 2018 have been presented in accordance with the standard, while results for prior periods have not been adjusted. The Company recognized $1.0 million and $1.0 million of operating lease assets and operating lease liabilities, respectively, on the Company’s balance sheets as of January 1, 2019, primarily related to the lease agreement for the Company’s principal executive office. Refer to Note 13 "Leases" for more information on the Company’s leases. In June 2016, the FASB issued ASU 2016-13 which requires financial instruments to be recognized at an estimate of current expected credit losses. As part of the ASU, financial assets measured at amortized cost will be presented at the net amount expected to be collected. In addition, companies will recognize an allowance for credit losses on available-for-sale investments rather than reducing the amortized cost in an other-than-temporary impairment. The standard is effective for public companies for fiscal years beginning after December 15, 2019, and interim periods within those years. The Company will adopt the standard effective January 1, 2020. The Company believes the adoption of this standard will have an immaterial impact on the Company’s accounting for its current financial instruments presented on the balance sheets at December 31, 2019; however, the Company will continue to evaluate the impact of this standard on its future financial instruments. In August 2018, the FASB issued ASU 2018-15 which includes provisions to clarify customer’s accounting for implementation costs incurred in a cloud computing arrangement. Under the updated guidance, a customer in a cloud computing arrangement that is a service contract should follow the internal-use software guidance to determine how to account for costs incurred in implementation. The updated guidance also requires certain classification on the balance sheets, statements of operations and statements of cash flows as well as additional quantitative and qualitative disclosures. The standard is effective for public companies for fiscal years beginning after December 15, 2019, and interim periods within those years. Entities can choose to adopt the new guidance prospectively or retrospectively. The ​ 2. Summary of Significant Accounting Policies (Continued) Company will adopt the standard effective January 1, 2020, and has chosen to adopt the standard prospectively. The Company does not believe the adoption of this standard to have a material impact to the Company’s balance sheets, statements of operations or statements of cash flows.

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies
Schedule of future minimum lease payments	The following table summarizes the Company’s estimated future minimum commitments as of December 31, 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Less than ​ ​ ​ ​ ​ ​ ​ More than ​ Total 1 Year 1 - 3 Years 3 - 5 Years 5 Years ​ ​ (in thousands) Revenue interest liability ​ $ 292,500 ​ $ — ​ $ — ​ $ — ​ $ 292,500 Operating leases ​ ​ 1,741 ​ ​ 538 ​ ​ 987 ​ ​ 216 ​ ​ — Total ​ $ 294,241 ​ $ 538 ​ $ 987 ​ $ 216 ​ $ 292,500

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Property and Equipment
Schedule of property and equipment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2018 ​ ​ (in thousands) Lab equipment ​ $ — ​ $ 232 Computer equipment ​ 256 ​ 51 Software ​ 615 ​ 205 Furniture, fixtures and other ​ 908 ​ 719 Leasehold improvements ​ 298 ​ 309 Assets in Progress ​ 99 ​ — Subtotal ​ 2,176 ​ 1,516 Less accumulated depreciation and amortization ​ 1,031 ​ 996 Property and equipment, net ​ $ 1,145 ​ $ 520 ​

Other Accrued Liabilities (Tabl

Other Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2019
Other Accrued Liabilities
Schedule of other accrued liabilities	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2018 ​ ​ (in thousands) Accrued compensation ​ $ 7,818 ​ $ 1,833 Accrued professional fees ​ 3,842 ​ ​ 1,228 Accrued franchise and property taxes ​ 37 ​ 44 Accrued other ​ 174 ​ 296 Total other accrued liabilities ​ $ 11,871 ​ $ 3,401

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2019
Investments
Schedule of Company's cash equivalents and investments	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 20,970 ​ $ — ​ $ — ​ $ 20,970 U.S. treasury notes ​ ​ 2,497 ​ ​ — ​ ​ — ​ ​ 2,497 Commercial paper ​ ​ 4,494 ​ ​ — ​ ​ — ​ ​ 4,494 Short-term investments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Certificates of deposit ​ ​ 245 ​ ​ — ​ ​ — ​ ​ 245 U.S. treasury notes ​ 29,155 ​ 23 ​ — ​ 29,178 Commercial paper ​ 5,228 ​ — ​ — ​ 5,228 Total ​ $ 62,589 ​ $ 23 ​ $ — ​ $ 62,612 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2018 ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cost Gains Losses Value ​ ​ (in thousands) Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 34,526 ​ $ — ​ $ — ​ $ 34,526 Short-term investments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Certificates of deposit ​ ​ 3,873 ​ ​ — ​ ​ (7) ​ ​ 3,866 U.S. treasury notes ​ 44,897 ​ — ​ (142) ​ 44,755 U.S. government agency securities ​ 50,598 ​ — ​ (169) ​ 50,429 Long-term investments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Certificates of deposit ​ 244 ​ — ​ (1) ​ 243 Total ​ $ 134,138 ​ $ — ​ $ (319) ​ $ 133,819 ​

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Measurements
Schedule of the Company's financial assets and liabilities that have been measured at fair value on a recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Description Total Level 1 Level 2 Level 3 ​ ​ (in thousands) December 31, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 20,970 ​ $ 20,970 ​ $ — ​ $ — Investments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Certificates of deposit ​ 245 ​ 245 ​ — ​ — U.S. treasury notes ​ 31,675 ​ 31,675 ​ — ​ — Commercial paper ​ 9,722 ​ — ​ 9,722 ​ — Total assets at fair value ​ $ 62,612 ​ $ 52,890 ​ $ 9,722 ​ $ — December 31, 2018 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Assets: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 34,526 ​ $ 34,526 ​ $ — ​ $ — Investments: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Certificates of deposit ​ 4,109 ​ 4,109 ​ — ​ — U.S. treasury notes ​ 44,755 ​ 44,755 ​ — ​ — U.S. government agency securities ​ 50,429 ​ — ​ 50,429 ​ — Total assets at fair value ​ $ 133,819 ​ $ 83,390 ​ $ 50,429 ​ $ —

Liability Related to the Reve_2

Liability Related to the Revenue Interest Purchase Agreement (Tables)	12 Months Ended
	Dec. 31, 2019
Liability Related to the Revenue Interest Purchase Agreement
Summary of revenue interest liability activity	The following table summarizes the revenue interest liability activity during the year ended December 31, 2019: ​ ​ ​ ​ ​ (in thousands) Revenue interest liability at June 26, 2019 ​ $ 125,000 Interest expense recognized ​ 8,120 Capitalized issuance costs ​ (576) Revenue interest liability at December 31, 2019 ​ $ 132,544

Stock Compensation (Tables)

Stock Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Stock Compensation
Summary of activity relating to the Company's options to purchase common stock	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ Remaining ​ ​ ​ ​ ​ Number of ​ Exercise Price ​ Contractual ​ Aggregate ​ Options Per Share Term (Years) Intrinsic Value ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) Outstanding at December 31, 2018 5,303,723 ​ $ 37.01 7.42 ​ $ 83,473 Granted 542,875 ​ $ 46.95 ​ ​ ​ ​ ​ Forfeited or cancelled (vested and unvested) (519,140) ​ $ 50.24 ​ ​ ​ ​ ​ Exercised (649,529) ​ $ 18.12 ​ ​ ​ ​ ​ Outstanding at December 31, 2019 4,677,929 ​ $ 39.31 6.82 ​ $ 109,054 ​
Summary of information about the Company's stock option plan	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ Remaining ​ ​ ​ ​ ​ Number of ​ Exercise Price ​ Contractual ​ Aggregate ​ Options Per Share Term (Years) Intrinsic Value ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) Vested and expected to vest at December 31, 2019 4,677,929 ​ $ 39.31 6.82 ​ $ 109,054 Exercisable at December 31, 2019 2,993,362 ​ $ 34.24 5.84 ​ $ 86,698 ​
Schedule of weighted-average assumptions used to compute the stock-based compensation costs for the stock options granted to employees	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Year ended ​ ​ December 31, ​ 2019 2018 2017 Risk-free interest rate 2.10 % 2.75 % 2.04 % Dividend yield — ​ — ​ — ​ Weighted-average expected life of options (years) 6.25 ​ 6.21 ​ 6.19 ​ Volatility 73 % 72 % 73 % ​ ​ 11. Stock Compensation (Continued)
Summary of activity relating to the Company's RSUs	​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Weighted-Average ​ RSUs Fair Value Per Share ​ ​ ​ ​ ​ ​ Outstanding and unvested at December 31, 2018 37,475 ​ $ 66.96 Granted 230,284 ​ $ 42.21 Forfeited or expired (4,083) ​ $ 36.73 Vested (17,710) ​ $ 64.71 Outstanding and unvested at December 31, 2019 245,966 ​ $ 44.45 ​

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases
Schedule of future maturities of operating lease liabilities	The following table summarizes the Company's future maturities of operating lease liabilities as of December 31, 2019: ​ ​ ​ ​ ​ (in thousands) 2020 ​ $ 538 2021 ​ 517 2022 ​ 470 2023 ​ 216 Total lease payments ​ 1,741 Less imputed interest ​ 178 Total ​ $ 1,563
Schedule of supplemental balance sheet information related to leases	The following table summarizes supplemental balance sheet information related to leases as of December 31, 2019: ​ ​ ​ ​ Operating Leases (in thousands) Right of use operating lease assets (long-term) ​ 1,532 Total right of use operating lease assets ​ $ 1,532 ​ ​ ​ ​ Operating lease liabilities (short-term) ​ $ 454 Operating lease liabilities (long-term) ​ 1,109 Total lease obligations under operating leases ​ $ 1,563

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Taxes
Schedule of reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2018 2017 Federal income tax (benefit) at statutory rate (21.0) % (21.0) % (34.0) % Change in tax rate (0.2) % 0.0 % 29.6 % Permanent items (1.0) % (0.5) % 0.1 % Other 0.7 % 0.5 % (0.9) % Amended Tax Returns ​ 0.0 % 0.0 % (4.5) % Change in valuation allowance 21.5 % 21.0 % 9.7 % Effective income tax rate 0.0 % 0.0 % 0.0 % ​
Schedule of significant components of the Company's deferred tax assets	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ 2019 2018 ​ ​ ​ (in thousands) Deferred tax assets: ​ ​ ​ ​ ​ ​ Federal and state operating loss carryforwards ​ $ 154,912 ​ $ 138,299 Equity compensation ​ ​ 17,217 ​ ​ 13,542 Temporary differences ​ 2,089 ​ 341 Total deferred tax assets ​ 174,218 ​ 152,182 Valuation allowance ​ (174,218) ​ (152,182) Net deferred tax assets ​ $ — ​ $ —

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2019
Net Loss Per Common Share
Schedule of the shares outstanding were excluded from the calculation of diluted net income (loss) per share due to their anti-dilutive effect	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ December 31, ​ 2019 2018 2017 Warrants for common stock — 8,230 ​ 185,353 Common shares under option 4,677,929 5,303,723 ​ 4,159,151 Unvested RSUs 245,966 37,475 ​ 10,003 Total potential dilutive shares 4,923,895 5,349,428 ​ 4,354,507

Statements of Cash Flows (Table

Statements of Cash Flows (Tables)	12 Months Ended
	Dec. 31, 2019
Statements of Cash Flows.
Schedule of reconciliation of cash and cash equivalents and restricted cash presented on the Condensed Balance Sheets to the same amounts presented on the Condensed Statements of Cash Flows	​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, December 31, ​ ​ 2019 ​ 2018 Cash and cash equivalents ​ $ 166,130 ​ $ 36,973 Restricted cash ​ 928 ​ — Total cash, cash equivalents and restricted cash shown on the statements of cash flows ​ $ 167,058 ​ $ 36,973

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Selected Quarterly Financial Data (Unaudited)
Schedule of unaudited quarterly financial data	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2019 ​ March 31 June 30 September 30 December 31 ​ ​ ​ (in thousands, except share and per share data) Revenues: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Collaboration revenue ​ $ 145,419 ​ $ 982 ​ $ 981 ​ $ 982 Total Revenues ​ 145,419 ​ 982 ​ 981 ​ 982 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Operating expenses: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Research and development ​ $ 46,308 ​ $ 42,788 ​ $ 48,281 ​ $ 38,234 General and administrative ​ 12,182 ​ 13,492 ​ 18,468 ​ 21,712 Total operating expenses ​ 58,490 ​ 56,280 ​ 66,749 ​ 59,946 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gain (loss) from operations: ​ 86,929 ​ (55,298) ​ (65,768) ​ (58,964) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Interest expense ​ — ​ — ​ (3,996) ​ (4,124) Other income, net ​ 450 ​ 1,077 ​ 1,387 ​ 1,142 Net gain (loss) ​ $ 87,379 ​ $ (54,221) ​ $ (68,377) ​ $ (61,946) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net gain (loss) per common share – basic (1) ​ $ 3.26 ​ $ (2.01) ​ $ (2.52) ​ $ (2.26) Net gain (loss) per common share – diluted ​ $ 3.07 ​ $ (2.01) ​ $ (2.52) ​ $ (2.26) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average shares outstanding - basic ​ ​ 26,842,785 ​ ​ 26,968,818 ​ ​ 27,171,769 ​ ​ 27,371,067 Weighted-average shares outstanding - diluted ​ 28,449,767 ​ 26,968,818 ​ 27,171,769 ​ 27,371,067 ​ ​ 17. Selected Quarterly Financial Data (Unaudited) (Continued) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2018 ​ March 31 June 30 September 30 December 31 ​ ​ (in thousands, except share and per share data) Operating expenses: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Research and development ​ $ 40,940 ​ $ 39,524 ​ $ 41,551 ​ $ 49,473 General and administrative ​ 5,954 ​ 6,956 ​ 9,011 ​ 11,176 Total operating expenses ​ 46,894 ​ 46,480 ​ 50,562 ​ 60,649 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Loss from operations: ​ (46,894) ​ (46,480) ​ (50,562) ​ (60,649) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Other income, net ​ 764 ​ 750 ​ 651 ​ 610 Net loss ​ $ (46,130) ​ $ (45,730) ​ $ (49,911) ​ $ (60,039) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss per common share - basic and diluted ​ $ (1.73) ​ $ (1.71) ​ $ (1.86) ​ $ (2.24) Weighted-average shares outstanding - basic and diluted ​ 26,605,189 ​ 26,786,796 ​ 26,804,026 ​ 26,818,331 (1) Due to the use of weighted average shares outstanding for each quarter for calculating net loss per common share, the sum of the quarterly net loss per common share amounts may not equal the net loss per common share amount for the full year.

The Company and Basis of Pres_2

The Company and Basis of Presentation (Details)	1 Months Ended
	Aug. 31, 2019item
The Company and Basis of Presentation
Number of patients enrolled in the global cardiovascular outcomes trial ("CVOT")	14,032

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2019USD ($)segment	Jan. 01, 2019USD ($)
Segment Information
Number of operating segments | segment	1
Impairment of Long-Lived Assets
Impairment losses	$ 0
Recent Accounting Pronouncements
Operating lease assets	1,532,000
Operating lease liabilities	$ 1,563,000
ASU 2016-02 | Adjustment
Recent Accounting Pronouncements
Operating lease assets		$ 1,000,000
Operating lease liabilities		$ 1,000,000
Property and equipment | Minimum
Property and Equipment, Net
Estimated useful lives	3 years
Property and equipment | Maximum
Property and Equipment, Net
Estimated useful lives	10 years

Collaborations with Third Par_2

Collaborations with Third Parties (Details) - USD ($) $ in Thousands	Jan. 02, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2019
Collaborations with Third Parties
Total Revenues		$ 982	$ 981	$ 982	$ 145,419	$ 148,364
License for the intellectual property
Collaborations with Third Parties
Total Revenues						144,400
Ongoing regulatory and development activities
Collaborations with Third Parties
Total Revenues						4,000
Regulatory performance obligations
Collaborations with Third Parties
Deferred revenue, Upfront payments		$ 1,600				$ 1,600
Collaborative Arrangement | Daiichi Sankyo Europe GmbH ("DSE")
Collaborations with Third Parties
Upfront cash payment	$ 150,000
Cash payment to the Company upon first commercial sales in the DSE Territory	$ 150,000
Collaborative Arrangement | Daiichi Sankyo Europe GmbH ("DSE") | Minimum
Collaborations with Third Parties
Percentage of royalties to be received on the net sales	15.00%
Collaborative Arrangement | Daiichi Sankyo Europe GmbH ("DSE") | Maximum
Collaborations with Third Parties
Percentage of royalties to be received on the net sales	25.00%

Warrants (Details)

Warrants (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Common stock
Warrants
Number of shares issued upon exercise of warrants		5,813	159,944	62,525
Warrants for common stock
Warrants
Warrants exercisable into stock (in shares)	8,230
Exercise price (in dollars per share)	$ 15.19
Fair value of warrants	$ 0.1
Number of warrants exercised		8,230	177,123	71,237
Warrants outstanding		0
Term A Loan
Warrants
Maximum borrowing capacity	5
Term A Loan | Secured promissory notes
Warrants
Proceeds from issuance of debt	$ 5

Commitments and Contingencies -

Commitments and Contingencies - Revenue Interest Purchase Agreement (Details) - Revenue Interest Purchase Agreement (RIPA) - USD ($) $ in Millions	Jun. 26, 2019	Dec. 31, 2019
Revenue Interest Purchase Agreement
Theoretical amount of net sales generated to illustrate estimated payments at the initial repayment rate in the first year		$ 100
The maximum of future aggregate annual net sales threshold for repayment obligation at the initial stated repayment rate as per agreement in the first year.		250
Illustrated estimated payments at the initial repayment rate based on a theoretical amount of net sales generated in the first year		7.5
Minimum
Revenue Interest Purchase Agreement
Future payments under revenue interest purchase agreement over the next year		0.1
Maximum
Revenue Interest Purchase Agreement
Future payments under revenue interest purchase agreement		$ 243.8
Oberland
Revenue Interest Purchase Agreement
Proceeds from revenue interest liability	$ 125
Amount of subsequent installment, subject to regulatory approval	25
Amount of subsequent installment, subject to achievement of Sales Threshold	$ 50
Revenue interest rate which will take effect if annual net sales equals or exceeds the Sales Threshold by December 31, 2021	2.50%
Initial revenue interest rate	7.50%
Percentage of revenue rights to be reacquired upon repayment completion	100.00%

Commitments and Contingencies_2

Commitments and Contingencies - Leases (Details) - Principal executive offices	Jul. 06, 2018USD ($)ft²	Feb. 28, 2014
Leases
Operating Lease term	60 months	63 months
Operating lease, period for increase of fixed monthly rent		12 months
Operating lease, period after which monthly rent increase		3 months
Current rentable square feet of office space | ft²	7,941
Increase in rentable square feet of office space | ft²	11,471
Base rent in first month	$ 0
Base rate in second month	15,990
Base rent thereafter	$ 19,412

Commitments and Contingencies_3

Commitments and Contingencies - Future Minimum Commitments (Details) $ in Thousands	Dec. 31, 2019USD ($)
Revenue Interest Liability, Payments Due
More than 5 Years	$ 292,500
Total	292,500
Future maturities of operating lease liabilities
Less than 1 Year	538
1 - 3 Years	987
3 - 5 Years	216
Total lease payments	1,741
Total future minimum lease payments
Less than 1 Year	538
1-3 Years	987
3-5 Years	216
More than 5 Years	292,500
Total	$ 294,241

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property and Equipment
Property and equipment, gross	$ 2,176	$ 1,516
Less accumulated depreciation and amortization	1,031	996
Property and equipment, net	1,145	520
Depreciation expense	319	265	$ 258
Lab equipment
Property and Equipment
Property and equipment, gross		232
Computer equipment
Property and Equipment
Property and equipment, gross	256	51
Software
Property and Equipment
Property and equipment, gross	615	205
Furniture, fixtures and other
Property and Equipment
Property and equipment, gross	908	719
Leasehold improvements
Property and Equipment
Property and equipment, gross	298	$ 309
Assets in Progress
Property and Equipment
Property and equipment, gross	$ 99

Other Accrued Liabilities (Deta

Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Other Accrued Liabilities
Accrued compensation	$ 7,818	$ 1,833
Accrued professional fees	3,842	1,228
Accrued franchise and property taxes	37	44
Accrued other	174	296
Total other accrued liabilities	$ 11,871	$ 3,401

Investments (Details)

Investments (Details) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments
Total, Amortized Cost	$ 62,589,000				$ 62,589,000	$ 134,138,000
Gross Unrealized Gains	23,000				23,000
Gross Unrealized Losses						(319,000)
Total, Estimated Fair Value	62,612,000				62,612,000	133,819,000
Amortization (accretion) of premiums and discounts on investments					(200,000)	(217,000)	$ 334,000
Other income, net	1,142,000	$ 1,387,000	$ 1,077,000	$ 450,000	4,056,000	2,803,000	2,192,000
Interest Income
Investments
Interest income on investments					3,700,000	2,600,000	2,500,000
Other income, net
Investments
Amortization (accretion) of premiums and discounts on investments					(300,000)	(200,000)	$ 300,000
Reclassification out of accumulated other comprehensive income (loss)
Investments
Other income, net					0
Short-term investments | Certificates of deposit
Investments
Investments, Amortized Cost	245,000				245,000	3,873,000
Gross Unrealized Losses						(7,000)
Investments, Estimated Fair Value	245,000				245,000	3,866,000
Short-term investments | U.S. treasury notes
Investments
Investments, Amortized Cost	29,155,000				29,155,000	44,897,000
Gross Unrealized Gains	23,000				23,000
Gross Unrealized Losses						(142,000)
Investments, Estimated Fair Value	29,178,000				29,178,000	44,755,000
Short-term investments | U.S. government agency securities
Investments
Investments, Amortized Cost						50,598,000
Gross Unrealized Losses						(169,000)
Investments, Estimated Fair Value						50,429,000
Short-term investments | Commercial paper
Investments
Investments, Amortized Cost	5,228,000				5,228,000
Investments, Estimated Fair Value	5,228,000				5,228,000
Long-term investments | Certificates of deposit
Investments
Investments, Amortized Cost						244,000
Gross Unrealized Losses						(1,000)
Investments, Estimated Fair Value						243,000
Money market funds
Investments
Cash equivalents	20,970,000				20,970,000	34,526,000
Cash equivalents, Estimated Fair Value	20,970,000				20,970,000	$ 34,526,000
U.S. treasury notes
Investments
Cash equivalents	2,497,000				2,497,000
Cash equivalents, Estimated Fair Value	2,497,000				2,497,000
Commercial paper
Investments
Cash equivalents	4,494,000				4,494,000
Cash equivalents, Estimated Fair Value	$ 4,494,000				$ 4,494,000

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Assets:
Total, Estimated Fair Value	$ 62,612	$ 133,819
Transfer of assets between levels	0	0
Transfer of liabilities between levels	0	0
Revenue Interest Purchase Agreement (RIPA) | Oberland
Liabilities:
Fair value of the revenue interest liability	132,500
Recurring fair value measurement
Assets:
Money market funds	20,970	34,526
Total, Estimated Fair Value	62,612	133,819
Recurring fair value measurement | Certificates of deposit
Assets:
Investments, Fair Value Disclosure	245	4,109
Recurring fair value measurement | U.S. treasury notes
Assets:
Investments, Fair Value Disclosure	31,675	44,755
Recurring fair value measurement | U.S. government agency securities
Assets:
Investments, Fair Value Disclosure		50,429
Recurring fair value measurement | Commercial paper
Assets:
Investments, Fair Value Disclosure	9,722
Recurring fair value measurement | Level 1
Assets:
Money market funds	20,970	34,526
Total, Estimated Fair Value	52,890	83,390
Recurring fair value measurement | Level 1 | Certificates of deposit
Assets:
Investments, Fair Value Disclosure	245	4,109
Recurring fair value measurement | Level 1 | U.S. treasury notes
Assets:
Investments, Fair Value Disclosure	31,675	44,755
Recurring fair value measurement | Level 2
Assets:
Total, Estimated Fair Value	9,722	50,429
Recurring fair value measurement | Level 2 | U.S. government agency securities
Assets:
Investments, Fair Value Disclosure		$ 50,429
Recurring fair value measurement | Level 2 | Commercial paper
Assets:
Investments, Fair Value Disclosure	$ 9,722

Liability Related to the Reve_3

Liability Related to the Revenue Interest Purchase Agreement - Summary (Details) - USD ($) $ in Thousands	Jun. 26, 2019	Dec. 31, 2019	Dec. 31, 2019
Liability Related to the Revenue Interest Purchase Agreement
Revenue interest liability at June 26, 2019		$ 127,308	$ 127,308
Revenue Interest Purchase Agreement (RIPA)
Liability Related to the Revenue Interest Purchase Agreement
Theoretical amount of net sales generated to illustrate estimated payments at the initial repayment rate in the first year			100,000
The maximum of future aggregate annual net sales threshold for repayment obligation at the initial stated repayment rate as per agreement in the first year.			250,000
Illustrated estimated payments at the initial repayment rate based on a theoretical amount of net sales generated in the first year			7,500
Revenue interest liability at June 26, 2019	$ 125,000
Interest expense recognized		8,120	8,100
Capitalized issuance costs		(576)	(600)
Revenue interest liability at December 31, 2019		$ 132,544	$ 132,544
Revenue Interest Purchase Agreement (RIPA) | Oberland
Liability Related to the Revenue Interest Purchase Agreement
Proceeds from revenue interest liability	125,000
Total amount of subsequent installment, subject to RIPA terms and conditions	75,000
Amount of subsequent installment, subject to regulatory approval	25,000
Amount of subsequent installment, subject to achievement of Sales Threshold	50,000
Milestone amount for worldwide sales to receive the Third Payment	$ 100,000
Trailing number of months sales must be at or above milestone amount	6 months
Revenue interest rate which will take effect if annual net sales equals or exceeds the Sales Threshold by December 31, 2021	2.50%
Initial revenue interest rate	7.50%
Minimum amount of annual net sales to qualify for reduced revenue interest rate by December 31, 2021	$ 350,000
Percentage of invested capital received by December 31, 2024, to qualify for second reduced revenue interest rate	100.00%
Revenue interest rate if annual net sales equal or exceed the Sales Threshold and if the Purchasers receive 100% of their invested capital by December 31, 2024	0.40%
Percentage of increase in royalty rate upon drawdown of third payment	33.33%
Percentage of revenue interests payment on which agreement terminates	195.00%
Percentage of revenue interests payment on which agreement terminates, if prior to the anniversary of the closing date, if put option is exercised	120.00%
Percentage of revenue interests payment on which agreement terminates, prior to the third anniversary of the closing date, if put option is exercised	175.00%
Percentage of revenue interests payment on which agreement terminates, after the third anniversary of the closing date, if put option is exercised	195.00%
Effective annual imputed interest rate (as a percent)	12.60%
Revenue interest liability at June 26, 2019	$ 125,000

Stock Compensation - Summary of

Stock Compensation - Summary of Plans (Details) - shares	1 Months Ended	12 Months Ended
	May 31, 2015	Dec. 31, 2019	Nov. 30, 2019	May 31, 2017	Apr. 30, 2015
2017 Inducement Equity Plan
Stock compensation
Number of commons stock shares available for issuance			400,000	750,000
2013 Stock Option and Incentive Plan
Stock compensation
Increase in number of commons stock shares available for issuance	923,622
Number of commons stock shares available for issuance	2,975,000				2,051,378
Increase in common stock shares reserved and available for issuance, as a percentage of common stock shares outstanding	2.50%
2008 Incentive Stock Option and Restricted Stock Plan
Stock compensation
Grant period of stock awards		10 years
Purchase price expressed as a percentage of fair value of shares on the date of grant		100.00%
Vesting percentage on the first anniversary of the option grant		25.00%
Period for which remainder of grant amount will vest on the first day of each calendar quarter		3 years
Expiration period		10 years
Period from cessation of employment within which options expire if not exercised		90 days

Stock Compensation - Options (D

Stock Compensation - Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number of Options
Outstanding at the beginning of period (in shares)	5,303,723
Granted (in shares)	542,875
Forfeited or expired (in shares)	(519,140)
Exercised (in shares)	(649,529)
Outstanding at the end of the period (in shares)	4,677,929	5,303,723
Weighted-Average Exercise Price Per Share
Outstanding at the beginning of period (in dollars per share)	$ 37.01
Granted (in dollars per share)	46.95
Forfeited or expired (in dollars per share)	50.24
Exercised (in dollars per share)	18.12
Outstanding at the end of the period (in dollars per share)	$ 39.31	$ 37.01
Weighted-Average Remaining Contractual Term (Years)
Outstanding	6 years 9 months 25 days	7 years 5 months 1 day
Aggregate Intrinsic Value
Outstanding	$ 109,054	$ 83,473
Information about the stock option plan
Number of Options, vested and expected to vest (in shares)	4,677,929
Number of Options, exercisable (in shares)	2,993,362
Weighted-Average Exercise Price Per Share, vested and expected to vest (in dollars per share)	$ 39.31
Weighted-Average Exercise Price Per Share, exercisable (in dollars per share)	$ 34.24
Weighted-Average Remaining Contractual Term, vested and expected to vest	6 years 9 months 25 days
Weighted-Average Remaining Contractual Term, exercisable	5 years 10 months 2 days
Aggregate Intrinsic Value, vested and expected to vest (in dollars)	$ 109,054
Aggregate Intrinsic Value, exercisable (in dollars)	86,698
Total intrinsic value of stock options exercised	$ 17,700	$ 12,100	$ 4,000
Valuation Assumptions for stock options
Risk-free interest rate (as a percent)	2.10%	2.75%	2.04%
Weighted-average expected life of options (years)	6 years 3 months	6 years 2 months 15 days	6 years 2 months 8 days
Volatility (as a percent)	73.00%	72.00%	73.00%
Additional disclosures
Weighted-average grant-date fair value (in dollars per share)	$ 31.18	$ 37.56	$ 15.99
Unrecognized stock-based compensation expense, options	$ 48,600
Stock options
Additional disclosures
Stock-based compensation expense	$ 23,500	$ 23,400	$ 18,200
Weighted-average period over which remaining unrecognized compensation cost will be recognized	2 years 7 months 6 days

Stock Compensation - RSUs (Deta

Stock Compensation - RSUs (Details) - RSUs - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number of RSUs
Outstanding and unvested at the beginning of period (in shares)	37,475
Granted (in shares)	230,284
Forfeited or expired (in shares)	(4,083)
Vested (in shares)	(17,710)
Outstanding and unvested at the ending of period (in shares)	245,966	37,475
Weighted-Average Fair Value Per Share
Outstanding and unvested at the beginning of period (in dollars per share)	$ 66.96
Granted (in dollars per share)	42.21
Forfeited or expired (in dollars per share)	36.73
Vested (in dollars per share)	64.71
Outstanding and unvested at the at the end of the period (in dollars per share)	$ 44.45	$ 66.96
Stock-based compensation expense	$ 2.4	$ 0.6	$ 0.4
Unrecognized stock-based compensation expense, RSUs	$ 9.2
Weighted-average period over which remaining unrecognized compensation cost will be recognized	3 years 1 month 6 days

Employee Benefit Plan (Details)

Employee Benefit Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Benefit Plan
Contributions to the 401(k) Plan	$ 0.7	$ 0.3	$ 0.3

Leases (Details)

Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 06, 2018	Feb. 28, 2014
Leases
Operating lease costs	$ 300
Cash paid for the amounts included in the measurement of lease liabilities	$ 300
Weighted-average remaining lease term of operating leases	3 years 3 months 18 days
Weighted average discount rate	6.50%
Right of use assets obtained in exchange for lease obligations	$ 0
Rent expense (Topic 840)		$ 300	$ 200
Future maturities of operating lease liabilities
2020	538
2021	517
2022	470
2023	216
Total lease payments	1,741
Less imputed interest	178
Total	1,563
Supplemental balance sheet information related to leases
Right of use operating lease assets (long-term)	1,532
Total right of use operating lease assets	1,532
Operating lease liabilities (short-term)	454
Operating lease liabilities (long-term)	1,109
Total lease obligations under operating leases	$ 1,563
Principal executive offices
Leases
Operating Lease term				60 months	63 months
Automobile leases and IT equipment leases
Leases
Operating Lease term	3 years

Income Taxes - Summary (Details

Income Taxes - Summary (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Provision for income taxes
Provision for income taxes	$ 0	$ 0	$ 0
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	21.00%	34.00%
Reduction in gross deferred tax assets			$ 50,400,000
Additional net income tax expense			0
Deferred tax assets
Deferred Tax Assets, Gross	$ 174,218,000	$ 152,182,000	99,800,000
Valuation allowance	174,218,000	152,182,000
Federal
Deferred tax assets
Net operating loss carryforwards	618,100,000	539,200,000	347,400,000
State
Deferred tax assets
Net operating loss carryforwards	$ 527,100,000	$ 526,600,000	$ 327,800,000

Income Taxes - Reconciliation (

Income Taxes - Reconciliation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate
Federal income tax (benefit) at statutory rate (as a percent)	(21.00%)	(21.00%)	(34.00%)
Change in tax rate (as a percent)	(0.20%)	(0.00%)	29.60%
Permanent items (as a percent)	(1.00%)	(0.50%)	0.10%
Other (as a percent)	0.70%	0.50%	(0.90%)
Amended Tax Returns (as a percent)	(0.00%)	(0.00%)	(4.50%)
Change in valuation allowance (as a percent)	21.50%	21.00%	9.70%
Effective income tax rate (as a percent)	0.00%	0.00%	0.00%
Unrecognized tax benefits related to interest and penalties accrued	$ 0

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Federal and state operating loss carryforwards	$ 154,912	$ 138,299
Equity compensation	17,217	13,542
Temporary differences	2,089	341
Total deferred tax assets	174,218	152,182	$ 99,800
Valuation allowance	(174,218)	(152,182)
Net deferred tax assets	$ 0	$ 0

Net Loss Per Common Share - Cal

Net Loss Per Common Share - Calculation of diluted net loss per share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Income (Loss) Per Common Share
Total potentially dilutive shares	4,923,895	5,349,428	4,354,507
Warrants for common stock
Net Income (Loss) Per Common Share
Total potentially dilutive shares		8,230	185,353
Stock options
Net Income (Loss) Per Common Share
Total potentially dilutive shares	4,677,929	5,303,723	4,159,151
Unvested RSUs
Net Income (Loss) Per Common Share
Total potentially dilutive shares	245,966	37,475	10,003

Statements of Cash Flows (Detai

Statements of Cash Flows (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statements of Cash Flows.
Cash and cash equivalents	$ 166,130	$ 36,973
Restricted cash	928
Total cash and cash equivalents and restricted cash shown on the Condensed Statements of Cash Flows	$ 167,058	$ 36,973	$ 34,468	$ 38,165

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Total Revenues	$ 982	$ 981	$ 982	$ 145,419					$ 148,364
Type of Revenue [Extensible List]	espr:CollaborationRevenueMember	espr:CollaborationRevenueMember	espr:CollaborationRevenueMember	espr:CollaborationRevenueMember					espr:CollaborationRevenueMember
Operating expenses:
Research and development	$ 38,234	$ 48,281	$ 42,788	$ 46,308	$ 49,473	$ 41,551	$ 39,524	$ 40,940	$ 175,611	$ 171,488	$ 147,603
General and administrative	21,712	18,468	13,492	12,182	11,176	9,011	6,956	5,954	65,854	33,097	21,379
Total operating expenses	59,946	66,749	56,280	58,490	60,649	50,562	46,480	46,894	241,465	204,585	168,982
Loss from operations	(58,964)	(65,768)	(55,298)	86,929	(60,649)	(50,562)	(46,480)	(46,894)	(93,101)	(204,585)	(168,982)
Interest expense	(4,124)	(3,996)							(8,120)	(28)	(198)
Other income, net	1,142	1,387	1,077	450					4,056	2,803	2,192
Other income, net					610	651	750	764
Net loss	$ (61,946)	$ (68,377)	$ (54,221)	$ 87,379	$ (60,039)	$ (49,911)	$ (45,730)	$ (46,130)	$ (97,165)	$ (201,810)	$ (166,988)
Earnings Per Share, Basic	$ (2.26)	$ (2.52)	$ (2.01)	$ 3.26
Earnings Per Share, Diluted	$ (2.26)	$ (2.52)	$ (2.01)	$ 3.07
Weighted Average Number of Shares Outstanding, Basic	27,371,067	27,171,769	26,968,818	26,842,785
Weighted Average Number of Shares Outstanding, Diluted	27,371,067	27,171,769	26,968,818	28,449,767
Net loss per common share (basic and diluted)					$ (2.24)	$ (1.86)	$ (1.71)	$ (1.73)	$ (3.59)	$ (7.54)	$ (6.98)
Weighted-average shares outstanding (basic and diluted) (in shares)					26,818,331	26,804,026	26,786,796	26,605,189	27,090,284	26,754,308	23,933,273