Arena Pharmaceuticals (ARNA) 10-Q 9 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 03, 2019
Document And Entity Information [Abstract]
Entity Registrant Name	ARENA PHARMACEUTICALS INC
Trading Symbol	ARNA
Entity Central Index Key	0001080709
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		49,570,066

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 727,404	$ 161,037
Short-term investments, available-for-sale	376,911	284,594
Accounts receivable	3,083	5,086
Prepaid expenses and other current assets	18,520	10,008
Total current assets	1,125,918	460,725
Investments, available-for-sale	165,354	82,412
Land, property and equipment, net	23,445	23,114
Deferred tax assets		110,333
Other non-current assets	15,336	10,319
Total assets	1,330,053	686,903
Current liabilities:
Accounts payable and other accrued liabilities	20,148	16,181
Accrued clinical and preclinical study fees	8,151	10,454
Current portion of lease financing obligations	3,410	3,283
Total current liabilities	31,709	29,918
Other long-term liabilities	6,368	1,301
Lease financing obligations, less current portion	48,539	49,426
Commitments and contingencies
Stockholders' equity:
Common stock	5	5
Additional paid-in capital	2,123,348	2,106,960
Accumulated other comprehensive income (loss)	502	(155)
Accumulated deficit	(880,418)	(1,500,552)
Total stockholders' equity	1,243,437	606,258
Total liabilities and stockholders' equity	$ 1,330,053	$ 686,903

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues:
Total revenues	$ 801,057	$ 1,755
Operating Costs and Expenses:
Research and development	45,396	21,573
General and administrative	16,578	11,151
Transaction costs	14,573
Total operating costs and expenses	76,547	32,724
Income (loss) from operations	724,510	(30,969)
Interest and Other Income (Expense):
Interest income	6,487	774
Interest expense	(1,241)	(1,472)
Other income	711	534
Total interest and other income (expense), net	5,957	(164)
Income (loss) from continuing operations before income taxes	730,467	(31,133)
Income tax provision	(110,333)
Income (loss) from continuing operations	620,134	(31,133)
Loss from discontinued operations		(830)
Net income (loss)	$ 620,134	$ (31,963)
Net income (loss) per share, basic:
Continuing operations	$ 12.53	$ (0.78)
Discontinued operations		(0.02)
Net income (loss) per share, basic	12.53	(0.80)
Net income (loss) per share, diluted:
Continuing operations	12.10	(0.78)
Discontinued operations		(0.02)
Net income (loss) per share, diluted	$ 12.10	$ (0.80)
Shares used in calculating net income (loss) per share, basic:	49,478	39,996
Shares used in calculating net income (loss) per share, diluted:	51,255	39,996
Comprehensive Income (Loss):
Net income (loss)	$ 620,134	$ (31,963)
Foreign currency translation gain (loss)	(19)	17
Unrealized gain (loss) on available-for-sale investments	676	(144)
Comprehensive income (loss)	620,791	(32,090)
Royalty Revenue
Revenues:
Total revenues	973	727
Collaboration and Other Revenue
Revenues:
Total revenues	84	$ 1,028
United Therapeutics | Collaboration and License Revenue
Revenues:
Total revenues	$ 800,000

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Underwriters	Common Stock	Common StockUnderwriters	Additional Paid-In Capital	Additional Paid-In CapitalUnderwriters	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning Balance at Dec. 31, 2017	$ 207,144		$ 4		$ 1,698,543		$ (1,216)	$ (1,490,187)
Beginning Balance (in shares) at Dec. 31, 2017			39,280,687
Adoption of ASC Topic 606 | ASC 606	20,136						1,102	19,034
Issuance of common stock to underwriters, net		$ 383,148		$ 1		$ 383,147
Issuance of common stock to underwriters, net (in shares)				9,775,000
Issuance of common stock upon exercise of options	1,919				1,919
Issuance of common stock upon exercise of options (in shares)			112,550
Issuance of common stock upon vesting of restricted stock unit awards	(166)				(166)
Issuance of common stock upon vesting of restricted stock unit awards (in shares)			28,448
Share-based compensation expense	4,044				4,044
Unrealized gain (loss) on available-for-sale investments	(144)						(144)
Translation gain (loss)	17						17
Net income (loss)	(31,963)							(31,963)
Ending Balance at Mar. 31, 2018	584,135		$ 5		2,087,487		(241)	(1,503,116)
Ending Balance (in shares) at Mar. 31, 2018			49,196,685
Beginning Balance at Dec. 31, 2018	606,258		$ 5		2,106,960		(155)	(1,500,552)
Beginning Balance (in shares) at Dec. 31, 2018			49,422,991
Issuance of common stock upon exercise of options	3,364				3,364
Issuance of common stock upon exercise of options (in shares)			125,655
Share-based compensation expense	13,024				13,024
Unrealized gain (loss) on available-for-sale investments	676						676
Translation gain (loss)	(19)						(19)
Net income (loss)	620,134							620,134
Ending Balance at Mar. 31, 2019	$ 1,243,437		$ 5		$ 2,123,348		$ 502	$ (880,418)
Ending Balance (in shares) at Mar. 31, 2019			49,548,646

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating Activities:
Net income (loss)	$ 620,134	$ (31,963)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Loss from discontinued operations		830
Depreciation and amortization	764	949
Deferred income taxes	110,333
Share-based compensation	13,024	4,033
Amortization of prepaid financing costs	22	28
Amortization of original issue discounts, net of premiums, on available-for-sale investments	(1,147)	(172)
Changes in operating assets and liabilities:
Accounts receivable	2,003	661
Prepaid expenses and other assets	(8,169)	613
Payables and accrued liabilities	1,080	(3,438)
Deferred revenues		(446)
Deferred rent	(394)	(274)
Net cash provided by (used in) operating activities - continuing operations	737,650	(29,179)
Net cash used in operating activities - discontinued operations		(601)
Net cash provided by (used in) operating activities	737,650	(29,780)
Investing Activities:
Purchases of available-for-sale investments	(249,525)	(25,477)
Proceeds from sale and maturity of available-for-sale investments	76,088	25,005
Purchases of property and equipment	(1,095)	(325)
Other non-current assets		(2)
Net cash used in investing activities - continuing operations	(174,532)	(799)
Net cash provided by investing activities - discontinued operations		2,990
Net cash provided by (used in) investing activities	(174,532)	2,191
Financing Activities:
Principal payments on lease financing obligations	(760)	(960)
Proceeds from issuance of common stock, net	3,364	385,256
Net cash provided by financing activities	2,604	384,296
Effect of exchange rate changes on cash	(18)	597
Net increase in cash, cash equivalents and restricted cash	565,704	357,304
Cash, cash equivalents and restricted cash at beginning of period	161,900	159,700
Cash, cash equivalents and restricted cash at end of period	$ 727,604	$ 517,004

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	1. Basis of Presentation The accompanying unaudited condensed consolidated financial statements of Arena Pharmaceuticals, Inc. should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2018, as filed with the Securities and Exchange Commission, or SEC, from which we derived our condensed consolidated balance sheet as of December 31, 2018. The accompanying condensed consolidated financial statements have been prepared in accordance with US generally accepted accounting principles, or GAAP, for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, since they are interim statements, the accompanying condensed consolidated financial statements do not include all of the information and notes required by GAAP for complete financial statements. The accompanying condensed consolidated financial statements reflect all adjustments, consisting of normal recurring adjustments, that are, in the opinion of our management, necessary to a fair statement of the results for the interim periods presented. Interim results are not necessarily indicative of results for a full year. Pursuant to an asset purchase agreement with Siegfried Pharma AG and Siegfried AG, or collectively and individually, Siegfried, in March 2018 we completed a transaction to sell and assign to Siegfried, and Siegfried purchased and assumed from Arena GmbH, certain drug product finishing facility assets and know-how, including fixtures, equipment, other personal property and real estate assets located in Zofingen, Switzerland, and related contracts and certain related liabilities, or collectively, the Manufacturing Operations. In connection with this transaction, all of Arena GmbH’s approximately 50 employees transferred to Siegfried. We have excluded from our continuing operations for the comparative period presented in this report revenues and expenses associated with the disposed Manufacturing Operations, which are reported as discontinued operations. For the three months ended March 31, 2018, the loss from discontinued operations was $0.8 million. Liquidity. As of March 31, 2019, we had cash, cash equivalents and available-for-sale investments of approximately $1.3 billion. We believe our cash, cash equivalents and available-for-sale investments will be sufficient to fund our operations for at least the next 12 months. We will require substantial cash to achieve our objectives of discovering, developing and commercializing drugs, as this process typically takes many years and potentially hundreds of millions of dollars for an individual drug. We may not have adequate available cash, or assets that could be readily turned into cash, to meet these objectives in the long term. We will need to obtain significant funds under our existing collaborations, under new collaboration, licensing or other commercial agreements for one or more of our drug candidates, programs or patent portfolios, or from other potential sources of liquidity, which may include the sale of equity, issuance of debt or other transactions. Changes in Accounting Policies - Leases. Effective January 1, 2019, we adopted Leases issued by the Accounting Standards Board, or FASB. . As a result, we have changed our accounting policy for leases as detailed below. We implemented ASC 842 using the modified retrospective transition approach by applying the new standard to leases existing at the date of initial application. We used the effective date as our date of initial application. Therefore, we did not update the financial information and did not provide the disclosures required under the new standard for dates and periods before January 1, 2019. We applied ASC 842 using a package of practical expedients, which permitted us not to reassess under the new standard our prior conclusions about lease identification, lease classification and initial direct costs. We did not elect the use-of-hindsight or the practical expedient pertaining to land easements; the latter not being applicable to us Upon adoption of ASC 842, we recorded an operating lease liability of $6.3 million with a corresponding right-of-use asset of $5.9 million based on the present value of the remaining minimum rental payments under the terms of our existing operating lease pertaining to one of our leased properties. Adoption of this standard did not have a material impact on our condensed consolidated statements of operations or cash flows. The new standard also provides practical expedients for an entity’s ongoing accounting. We elected the short-term lease recognition exemption for our office equipment leases and short-term office space leases. This means, for those leases that qualify, we do not recognize right-of-use assets or lease liabilities. See Note 10 for disclosures related to our leases. Recent Accounting Pronouncements . Collaborative Arrangements (Topic 808)—Clarifying the Interaction between Topic 808 and Topic 606 Revenue from Contracts with Customers Use of Estimates. The preparation of financial statements in accordance with GAAP requires our management to make estimates and assumptions that affect the reported amounts (including assets, liabilities, revenues and expenses) and related disclosures. The amounts reported could differ under different estimates and assumptions. Contingencies. We disclose information regarding each material claim where the likelihood of a loss contingency is probable or reasonably possible. The ability to predict the ultimate outcome of such matters involves judgments, estimates and inherent uncertainties. The actual outcome of such matters could differ materially from management’s estimates. Concentrations of Credit Risk. Financial instruments, which potentially subject us to concentrations of credit risk, consist primarily of cash, cash equivalents and available-for-sale investments. We limit our exposure to credit loss by holding our cash primarily in US dollars or, from time to time, placing our cash and investments in US government, agency or government-sponsored enterprise obligations and in corporate debt instruments that are rated investment grade.

Cash, Cash Equivalents, and Res

Cash, Cash Equivalents, and Restricted Cash	3 Months Ended
	Mar. 31, 2019
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]
Cash, Cash Equivalents, and Restricted Cash	2. Cash, cash equivalents and restricted cash The following table provides a reconciliation of the components of cash, cash equivalents and restricted cash reported in the accompanying condensed consolidated balance sheets to the total of the amount presented in the condensed consolidated statements of cash flows, in thousands: March 31, December 31, 2019 2018 Cash and cash equivalents $ 727,404 $ 161,037 Restricted cash included in other non-current assets 200 863 Total cash, cash equivalents and restricted cash presented in the condensed consolidated statement of cash flows $ 727,604 $ 161,900 The restricted cash relates to our property leases. The restriction will lapse when the related leases expire.

Fair Value Disclosures

Fair Value Disclosures	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Disclosures	3. Fair Value Disclosures We measure our financial assets and liabilities at fair value, which is defined as the exit price, or the amount that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. We use the following three-level valuation hierarchy that maximizes the use of observable inputs and minimizes the use of unobservable inputs to value our financial assets and liabilities: Level 1 - Observable inputs such as unadjusted quoted prices in active markets for identical instruments. Level 2 - Quoted prices for similar instruments in active markets or inputs that are observable for the asset or liability, either directly or indirectly. Level 3 - Significant unobservable inputs based on our assumptions. The following tables present our valuation hierarchy for our financial assets and liabilities that are measured at fair value on a recurring basis, in thousands: Fair Value Measurements Using Balance Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) March 31, 2019: Assets: Money market funds(1) $ 656,849 $ 656,849 $ — $ — US government and government agency notes(2) 231,106 231,106 — — Corporate debt instruments(2) 317,158 — 317,158 — December 31, 2018: Assets: Money market funds(1) $ 62,438 $ 62,438 $ — $ — US government and government agency notes(2) 171,278 171,278 — — Corporate debt instruments(2) 240,481 — 240,481 — (1) Included in cash and cash equivalents in the accompanying (2) Included in either cash and cash equivalents or available-for-sale investments in the accompanying condensed consolidated balance sheets.

Investments, Available-for-Sale

Investments, Available-for-Sale	3 Months Ended
	Mar. 31, 2019
Investments Debt And Equity Securities [Abstract]
Investments, Available-for-Sale	4. Investments, Available-for-Sale I nvestments, available-for-sale, consisted of the following Maturity in years Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value March 31, 2019: US government and government agency notes < 1 $ 179,579 $ 40 $ (4 ) $ 179,615 Corporate debt securities < 1 197,167 145 (16 ) 197,296 Short-term investments, available-for-sale $ 376,746 $ 185 $ (20 ) $ 376,911 US government and government agency notes 1 – 5 $ 51,461 $ 33 $ (3 ) $ 51,491 Corporate debt securities 1 – 5 113,628 237 (2 ) 113,863 Investments, available-for-sale $ 165,089 $ 270 $ (5 ) $ 165,354 December 31, 2018: US government and government agency notes < 1 $ 139,274 $ — $ (18 ) $ 139,256 Corporate debt securities < 1 145,468 — (130 ) 145,338 Short-term investments, available-for-sale $ 284,742 $ — $ (148 ) $ 284,594 US government and government agency notes 1 – 5 $ 16,998 $ 6 $ — $ 17,004 Corporate debt securities 1 – 5 65,512 — (104 ) 65,408 Investments, available-for-sale $ 82,510 $ 6 $ (104 ) $ 82,412

Land, Property and Equipment

Land, Property and Equipment	3 Months Ended
	Mar. 31, 2019
Property Plant And Equipment [Abstract]
Land, Property and Equipment	5. Land, Property and Equipment Land, property and equipment consisted of the following, in thousands: March 31, December 31, 2019 2018 Cost $ 70,637 $ 69,542 Less accumulated depreciation and amortization (47,192 ) (46,428 ) Land, property and equipment, net $ 23,445 $ 23,114

Accounts Payable and Other Accr

Accounts Payable and Other Accrued Liabilities	3 Months Ended
	Mar. 31, 2019
Payables And Accruals [Abstract]
Accounts Payable and Other Accrued Liabilities	6. Accounts Payable and Other Accrued Liabilities Accounts payable and other accrued liabilities consisted of the following, in thousands: March 31, December 31, 2019 2018 Accounts payable $ 1,643 $ 6,192 Accrued expenses 12,070 — Accrued compensation 3,700 8,622 Other accrued liabilities 2,735 1,367 Total accounts payable and other accrued liabilities $ 20,148 $ 16,181

Collaborations and License Agre

Collaborations and License Agreements	3 Months Ended
	Mar. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaborations and License Agreements	7. Collaborations and License Agreements We have collaborations or license agreements with the following companies: United Therapeutics Corporation, or United Therapeutics, Everest Medicines Limited, Eisai Co., Ltd. and Eisai Inc., or collectively, Eisai, Boehringer Ingelheim International GmbH, or Boehringer Ingelheim, Outpost Medicine, LLC, and Axovant Sciences GmbH, or Axovant Previously, we had a toll manufacturing agreement with Siegfried. Refer to our Annual Report on Form 10-K for the year ended December 31, 2018, for more information on our significant collaboration and license agreements. In the following table, revenue is disaggregated by major customers, timing of revenue recognition and revenue classification, in thousands. Three Months Ended March 31, 2019 2018 Customers United Therapeutics $ 800,000 $ — Eisai 823 2,228 Boehringer Ingelheim 84 460 Axovant — 568 Siegfried — 942 Other 150 64 Total $ 801,057 $ 4,262 Timing of revenue recognition Revenue recognized at a point in time $ 800,150 $ 1,755 Revenue recognized over time 907 2,507 Total $ 801,057 $ 4,262 Classification Revenue from continuing operations $ 801,057 $ 1,755 Revenue reported under discontinued operations — 2,507 Total $ 801,057 $ 4,262 The following table provides detail of changes in our contract assets, in thousands: Contract Assets - Current Contract Assets - Non-Current Balances at December 31, 2018 $ 1,484 $ 4,471 Reductions of contract assets (18 ) (326 ) Balances at March 31, 2019 $ 1,466 $ 4,145 United Therapeutics Corporation. In November 2018, we entered into an exclusive license agreement, or the United Therapeutics Agreement, with United Therapeutics. Under the United Therapeutics Agreement, we granted United Therapeutics an exclusive, worldwide, royalty-bearing license to develop, manufacture and commercialize ralinepag in any formulation. This transaction was completed on January 24, 2019. Under the United Therapeutics Agreement, United Therapeutics is responsible for all development, manufacturing and commercialization of the licensed products globally. In connection with this transaction we incurred transaction fees of approximately $17.0 million, of which $14.6 million was incurred in the three months ended March 31, 2019, and is presented as transaction costs in the condensed consolidated statement of operations. Under the United Therapeutics Agreement of $800.0 million. to an aggregate of $400.0 million in regulatory milestone payments related to ralinepag, consisting of a payment of $150.0 million upon first marketing approval of an oral formulation of ralinepag in a major non-U.S. market, and a payment of $250.0 million upon U.S. marketing approval of an inhaled formulation of ralinepag to treat pulmonary arterial hypertension, as well as low double-digit, tiered royalties on net sales of ralinepag products, subject to certain adjustments for third party license payments. The promised goods and services under the United Therapeutics United Therapeutics A United Therapeutics Eisai. In December 2016, we and Eisai amended and restated the terms of the previous marketing and supply agreement for lorcaserin with Eisai by entering into a Transaction Agreement and a Supply Agreement (collectively, the Eisai Agreement) with Eisai. Under the Transaction Agreement, Eisai acquired an exclusive royalty-bearing license or transfer of intellectual property to global commercialization and manufacturing rights to lorcaserin, including in the territories retained by us under the prior agreement, with control over global development and commercialization decisions. Eisai is responsible for all lorcaserin development expenses going forward. We also assigned to Eisai our rights under the commercial lorcaserin distribution agreements with Ildong Pharmaceutical Co., Ltd., or Ildong, for South Korea; CY Biotech Company Limited, or CYB, for Taiwan; and Teva Pharmaceuticals Ltd.’s Israeli subsidiary, Abic Marketing Limited, or Teva, for Israel. Under the Supply Agreement, Eisai paid us for finished drug product plus monthly manufacturing support payments through March 2018 totaling CHF 8.7 million. We manufactured lorcaserin until March 31, 2018, when we sold our Manufacturing Operations. Revenues earned for (i) lorcaserin sold by us to Eisai under the manufacturing and supply commitment within the Supply Agreement and (ii) the manufacturing support payments are classified within discontinued operations as part of the Manufacturing Operations in the condensed consolidated statements of operations. All other revenues earned under the Transaction Agreement, such as royalties, are classified within continuing operations in the condensed consolidated statements of operations. Pursuant to the Transaction Agreement, we are eligible to receive royalty payments from Eisai based on the global net sales of lorcaserin. The royalty rates are as follows: • 9.5% on annual net sales less than or equal to $175.0 million • 13.5% on annual net sales greater than $175.0 million but less than or equal to $500.0 million • 18.5% of annual net sales greater than $500.0 million We are eligible to receive an additional sales-based milestone of $25.0 million upon the achievement of global net sales of lorcaserin for a calendar year first exceeding $250.0 million. The promised goods and services under the Eisai Agreement were assessed in combination with promised goods and services under our previous agreements with Eisai and commercial lorcaserin distribution agreements with Ildong, CYB, and Teva. The total estimated transaction price of these contracts included previously received upfront payments, milestone payments, proceeds from net products sales, reimbursement of development expenses, reimbursement of patent expenses, manufacturing support payments received under the Supply Agreement, proceeds from the sale of inventory of bulk lorcaserin and the precursor material. e recognized a contract asset related to estimated future royalty payments from intellectual property sold to Eisai under the Transaction Agreement. intellectual property sold to Eisai under the Transaction Agreement. For the three months ended March 31, 2019, and 2018, we recorded royalty revenue of $0.8 million and $0.7 million, respectively, related to the Transaction Agreement. For the three months ended March 31, 2018, we recognized as revenue $1.5 million, classified within discontinued operations, related to the Supply Agreement, primarily consisting of net product sales and other collaboration revenue with no such revenue recorded during the three months ended March 31, 2019.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	8. Income Taxes We calculate the interim income tax provision in accordance with Accounting Standard Codification Topic 270, Interim Reporting Accounting for Income Taxes,

Share-based Compensation

Share-based Compensation	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-based Compensation	9. Share-based Compensation We recognized share-based compensation expense as follows, in thousands: Three months ended March 31, 2019 2018 Research and development $ 6,707 $ 1,650 General and administrative 6,317 2,383 Discontinued operations — 11 Total share-based compensation expense $ 13,024 $ 4,044 The following table summarizes our stock option activity during the three months ended March 31, 2019, in thousands (except per share data): Options Weighted- Average Exercise Price Outstanding at January 1, 2019 6,541 $ 28.83 Granted 2,219 41.36 Exercised (125 ) 26.77 Forfeited/cancelled/expired (112 ) 28.70 Outstanding at March 31, 2019 8,523 $ 32.13 During the three months ended March 31, 2019, a total of 297,000 target Performance-Based Restricted Stock Units, or PRSUs, were granted to the employees in a company-wide grant. The PRSUs vest, if at all, upon the closing price of our common stock, or the Closing Price, reaching certain price thresholds during the three-year performance period beginning January 4, 2019, and ending January 3, 2022, or the Performance Period, and the participant’s subsequent satisfaction of a continuing service requirement of generally 90 calendar days. If, on five consecutive trading days or ten non-consecutive trading days during the Performance Period, the Closing Price equals or exceeds $60.00, $67.50 or $75.00, and the participant thereafter satisfies a continuing service requirement, then the PRSUs are deemed vested at 50%, 100% or 200%, respectively, of the participant’s respective target PRSU amount. The shares may be issued following achievement of each price threshold, and the maximum number of common shares that may be issued pursuant to each PRSU grant equals 200% of the number of PRSUs granted. As these awards contain a market condition, we used a Monte Carlo simulation model to estimate the grant-date fair value, which totaled $18.1 million. The grant-date fair value is recognized as compensation expense over the requisite service period of approximately 1.2 years which was derived from the Monte Carlo simulation; no compensation expense is recognized for service not provided in case of separation from the Company. There is no adjustment of compensation expense recognized for service performed regardless of the number of PRSUs, if any, that ultimately vest. During the three months ended March 31, 2018, 32,322 granted in March 2015 based on the TSR, of our common stock relative to the TSR of the Nasdaq Biotechnology Index over the three-year performance period that began on March 1, 2015

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases	10. Leases We have three properties in San Diego, California, under sale and leaseback agreements. The terms of these leases contain a purchase option and stipulate annual increases in monthly rental payments of 2.5%. We account for our sale and leaseback transactions using the financing method. Under the financing method, the book value of the properties and related accumulated depreciation remain on our balance sheet and no sale is recognized. The adoption of ASC 842 did not result in a change to our current accounting policy for our sale and leaseback agreements. The sales price of the properties is recorded as a financing obligation, and a portion of each lease payment is recorded as interest expense. We recorded interest expense of $1.2 million, and $1.5 million for the three months ended March 31, 2019, and 2018, respectively, related to these leases. We expect interest expense related to our facilities to total $26.0 million from December 31, 2018, through the remaining terms of the leases until their expiration in May 2027. The aggregate residual value of the facilities at the end of the lease terms is $5.0 million. We lease an additional property in San Diego, California, under an operating lease, which expires in May 2027, contains a purchase option and stipulates annual increases in monthly rental payments of 2.5%. Upon adoption of ASC 842, we recorded an operating lease liability of $6.3 million with a corresponding right-of-use asset of $5.9 million based on the present value of the remaining minimum lease payments under the terms of our existing operating lease. As our leases do not provide an implicit rate, we used our incremental borrowing rate based on the information available at effective date of adoption in determining the present value of remaining minimum lease payments. The weighted-average discount rate we used was 7.25%. As of March 31, 2019, the balance of the right-of-use asset associated with this lease was $5.8 million and is included in other non-current assets in the accompanying condensed consolidated balance sheet. As of March 31, 2019, the current portion of the corresponding lease liability of $0.5 million is included in accounts payable and other accrued liabilities and the non-current portion of the lease liability of $5.7 million is included in other long-term liabilities in the accompanying condensed consolidated balance sheet. The operating lease costs and cash paid for the amounts included in the measurement of lease liabilities are classified as operating activities in the accompanying condensed consolidated cash flow statement. We also lease shared office space in Boston, Massachusetts, under a short-term lease arrangement and office space in Zug, Switzerland, under an operating lease which expires in September 2020. In March 2019, we entered into an additional lease in Zug, Switzerland, for approximately 10,500 square feet of office space with the lease inception date of June 1, 2019. We recognized rent expense of $0.3 million and $0.4 million for the three months ended March 31, 2019, and 2018, respectively. At March 31, 2019, the f uture lease payments under our existing financing obligations and non-cancellable operating leases were as follows, in thousands: Year ending December 31, Financing Obligations Operating Leases Remainder of 2019 $ 5,407 $ 812 2020 8,254 1,098 2021 8,461 976 2022 8,672 1,000 2023 8,889 1,025 2024 9,111 1,051 Thereafter 22,940 2,647 Total minimum lease payments 71,734 $ 8,609 Less amounts representing interest (24,735 ) Add amounts representing residual value 4,950 Lease financing obligations 51,949 Less current portion (3,410 ) $ 48,539 At December 31, 2018, the future minimum lease payments under our existing financing and operating lease obligations were as follows, in thousands: Year ending December 31, Financing Obligations Operating Leases 2019 $ 7,391 $ 1,050 2020 8,254 1,100 2021 8,461 976 2022 8,672 1,000 2023 8,889 1,025 Thereafter 32,052 3,698 Total minimum lease payments 73,719 $ 8,849 Less amounts representing interest (25,960 ) Add amounts representing residual value 4,950 Lease financing obligations 52,709 Less current portion (3,283 ) $ 49,426 In 2016 and 2017, we entered into agreements to sublease several of our California properties including an agreement to sublease one of our properties to Beacon Discovery, Inc., or Beacon, a variable interest entity. All our subleases expire in May 2027. The terms of the subleases stipulate annual increases in monthly rental payments. We recognized rent income from our subleases of $0.7 million and $0.6 million for the three months ended March 31, 2019, and 2018, respectively. At March 31, 2019, the expected minimum rental payments to be received under our subleases were as follows: Year ending December 31, Remainder of 2019 $ 1,175 2020 1,873 2021 2,477 2022 3,487 2023 3,794 2024 3,896 Thereafter 9,839 Total $ 26,541

Income (Loss) Per Share

Income (Loss) Per Share	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Income (Loss) Per Share	11. Income (Loss) Per Share We calculate basic and diluted income (loss) from continuing operations, loss from discontinued operations and net income (loss) per share using the weighted-average number of shares of common stock outstanding during the period. Since we have a loss from continuing operations for the three months ended March 31, 2018, in addition to excluding potentially dilutive out-of-the money securities, we have excluded from our calculation of diluted income (loss) per share all potentially dilutive in-the-money (i) stock options, (ii) restricted stock unit awards, or RSUs, and (iii) PRSUs, and our diluted net income (loss) per share is the same as our basic net income (loss) per share. The following table presents the weighted-average number of potentially dilutive securities that were excluded from our calculation of diluted net income (loss) per share, in thousands: Three months ended March 31, 2019 2018 Stock options 5,471 5,360 RSUs and unvested restricted stock — 25 Total 5,471 5,385

Legal Proceedings

Legal Proceedings	3 Months Ended
	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Legal Proceedings	12. Legal Proceedings On September 30, 2016, we and Eisai Inc. filed a patent infringement lawsuit against Lupin Limited and Lupin Pharmaceuticals, Inc. (collectively, Lupin) in the U.S. District Court for the District of Delaware. The lawsuit related to a “Paragraph IV certification” notification that we and Eisai Inc. received regarding an abbreviated new drug application, or ANDA, submitted to the FDA by Lupin requesting approval to engage in the commercial manufacture, use, importation, offer for sale or sale of a generic version of BELVIQ (lorcaserin hydrochloride tablets, 10 mg). In its notification, Lupin alleged that no valid, enforceable claim of any of the patents that are listed in the FDA’s Approved Drug Products with Therapeutic Equivalence Evaluations, or Orange Book, for BELVIQ would be infringed by Lupin’s manufacture, importation, use, sale or offer for sale of the product described in its ANDA for 10 mg lorcaserin hydrochloride tablets. Lupin was accused of infringing U.S. Patent Nos. 6,953,787; 7,514,422; 7,977,329; 8,207,158 and 8,273,734. On January 11, 2017, Lupin filed an answer, defenses and counterclaims to the September 30, 2016 complaint. We and Eisai Inc. filed an answer to Lupin’s counterclaims on February 1, 2017. On March 6, 2017, we and Eisai Inc. filed a patent infringement lawsuit against Teva Pharmaceuticals USA, Inc. and Teva Pharmaceutical Industries Ltd. (collectively, Teva) in the U.S. District Court for the District of Delaware. The lawsuit also related to a “Paragraph IV certification” notification that we and Eisai Inc. received regarding an ANDA submitted to the FDA by Teva requesting approval to engage in the commercial manufacture, use, importation, offer for sale or sale of a generic version of BELVIQ XR (lorcaserin hydrochloride extended-release tablets, 20 mg). In its notification, Teva alleged that no valid, enforceable claim of any of the patents that are listed in the Orange Book for BELVIQ XR would be infringed by Teva’s manufacture, importation, use, sale or offer for sale of the product described in its ANDA. Teva was accused of infringing U.S. Patent Nos. 6,953,787; 7,514,422; 7,977,329; 8,207,158 and 8,273,734. On April 18, 2017, Teva filed an amended answer, defenses and counterclaims to the March 6, 2017 complaint. On May 1, 2017, the Teva and Lupin actions were consolidated for all purposes and was set to follow the case schedule that was previously entered in the Lupin action. We and Eisai Inc. filed an answer to Teva’s amended counterclaims on May 3, 2017. On or about October 16, 2017, we and Eisai Inc. received a “Paragraph IV certification” notification from Teva alleging that no valid, enforceable claim of U.S. Patent No. 9,770,455, which was listed in the Orange Book for BELVIQ and BELVIQ XR We and Eisai Inc. also received a “Paragraph IV certification” notification from Lupin alleging that no valid, enforceable claim of any of the patents that are listed in the Orange Book for BELVIQ and BELVIQ XR would be infringed by Lupin’s manufacture, importation, use, sale or offer for sale of the product described in its ANDA for 20 mg lorcaserin hydrochloride extended-release tablets. On March 23, 2018, we and Eisai Inc. filed a second amended complaint against Lupin and Teva, adding infringement of U.S. Patent Nos. 6,953,787, 7,514,422, 7,977,329, 8,207,158, 8,273,734, and 9,770,455 by Lupin’s generic equivalent of BELVIQ XR. Trial in this consolidated action was scheduled for April 15, 2019. After the expert discovery phase of the case, Eisai entered into settlement agreements with Teva and Lupin, respectively, and we gave Teva and Lupin, respectively, certain covenants not to sue in view of the Eisai settlements. These respective litigations were accordingly dismissed without prejudice on March 5, 2019 (Teva) and April 4, 2019 (Lupin). The terms of the settlement agreements are confidential.

Basis of Presentation (Policies

Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements of Arena Pharmaceuticals, Inc. should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2018, as filed with the Securities and Exchange Commission, or SEC, from which we derived our condensed consolidated balance sheet as of December 31, 2018. The accompanying condensed consolidated financial statements have been prepared in accordance with US generally accepted accounting principles, or GAAP, for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, since they are interim statements, the accompanying condensed consolidated financial statements do not include all of the information and notes required by GAAP for complete financial statements. The accompanying condensed consolidated financial statements reflect all adjustments, consisting of normal recurring adjustments, that are, in the opinion of our management, necessary to a fair statement of the results for the interim periods presented. Interim results are not necessarily indicative of results for a full year. Pursuant to an asset purchase agreement with Siegfried Pharma AG and Siegfried AG, or collectively and individually, Siegfried, in March 2018 we completed a transaction to sell and assign to Siegfried, and Siegfried purchased and assumed from Arena GmbH, certain drug product finishing facility assets and know-how, including fixtures, equipment, other personal property and real estate assets located in Zofingen, Switzerland, and related contracts and certain related liabilities, or collectively, the Manufacturing Operations. In connection with this transaction, all of Arena GmbH’s approximately 50 employees transferred to Siegfried. We have excluded from our continuing operations for the comparative period presented in this report revenues and expenses associated with the disposed Manufacturing Operations, which are reported as discontinued operations. For the three months ended March 31, 2018, the loss from discontinued operations was $0.8 million.
Liquidity	Liquidity. As of March 31, 2019, we had cash, cash equivalents and available-for-sale investments of approximately $1.3 billion. We believe our cash, cash equivalents and available-for-sale investments will be sufficient to fund our operations for at least the next 12 months. We will require substantial cash to achieve our objectives of discovering, developing and commercializing drugs, as this process typically takes many years and potentially hundreds of millions of dollars for an individual drug. We may not have adequate available cash, or assets that could be readily turned into cash, to meet these objectives in the long term. We will need to obtain significant funds under our existing collaborations, under new collaboration, licensing or other commercial agreements for one or more of our drug candidates, programs or patent portfolios, or from other potential sources of liquidity, which may include the sale of equity, issuance of debt or other transactions.
Changes in Accounting Policies - Leases	Changes in Accounting Policies - Leases. Effective January 1, 2019, we adopted Leases issued by the Accounting Standards Board, or FASB. . As a result, we have changed our accounting policy for leases as detailed below. We implemented ASC 842 using the modified retrospective transition approach by applying the new standard to leases existing at the date of initial application. We used the effective date as our date of initial application. Therefore, we did not update the financial information and did not provide the disclosures required under the new standard for dates and periods before January 1, 2019. We applied ASC 842 using a package of practical expedients, which permitted us not to reassess under the new standard our prior conclusions about lease identification, lease classification and initial direct costs. We did not elect the use-of-hindsight or the practical expedient pertaining to land easements; the latter not being applicable to us Upon adoption of ASC 842, we recorded an operating lease liability of $6.3 million with a corresponding right-of-use asset of $5.9 million based on the present value of the remaining minimum rental payments under the terms of our existing operating lease pertaining to one of our leased properties. Adoption of this standard did not have a material impact on our condensed consolidated statements of operations or cash flows. The new standard also provides practical expedients for an entity’s ongoing accounting. We elected the short-term lease recognition exemption for our office equipment leases and short-term office space leases. This means, for those leases that qualify, we do not recognize right-of-use assets or lease liabilities. See Note 10 for disclosures related to our leases.
Recent Accounting Pronouncements	Recent Accounting Pronouncements . Collaborative Arrangements (Topic 808)—Clarifying the Interaction between Topic 808 and Topic 606 Revenue from Contracts with Customers
Use of Estimates	Use of Estimates. The preparation of financial statements in accordance with GAAP requires our management to make estimates and assumptions that affect the reported amounts (including assets, liabilities, revenues and expenses) and related disclosures. The amounts reported could differ under different estimates and assumptions.
Contingencies	Contingencies. We disclose information regarding each material claim where the likelihood of a loss contingency is probable or reasonably possible. The ability to predict the ultimate outcome of such matters involves judgments, estimates and inherent uncertainties. The actual outcome of such matters could differ materially from management’s estimates.
Concentrations of Credit Risk	Concentrations of Credit Risk. Financial instruments, which potentially subject us to concentrations of credit risk, consist primarily of cash, cash equivalents and available-for-sale investments. We limit our exposure to credit loss by holding our cash primarily in US dollars or, from time to time, placing our cash and investments in US government, agency or government-sponsored enterprise obligations and in corporate debt instruments that are rated investment grade.
Fair Value Measurements	We measure our financial assets and liabilities at fair value, which is defined as the exit price, or the amount that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. We use the following three-level valuation hierarchy that maximizes the use of observable inputs and minimizes the use of unobservable inputs to value our financial assets and liabilities: Level 1 - Observable inputs such as unadjusted quoted prices in active markets for identical instruments. Level 2 - Quoted prices for similar instruments in active markets or inputs that are observable for the asset or liability, either directly or indirectly. Level 3 - Significant unobservable inputs based on our assumptions.
Income Taxes	Income Taxes Interim Reporting Accounting for Income Taxes,
Income (Loss) Per Share	We calculate basic and diluted income (loss) from continuing operations, loss from discontinued operations and net income (loss) per share using the weighted-average number of shares of common stock outstanding during the period. Since we have a loss from continuing operations for the three months ended March 31, 2018, in addition to excluding potentially dilutive out-of-the money securities, we have excluded from our calculation of diluted income (loss) per share all potentially dilutive in-the-money (i) stock options, (ii) restricted stock unit awards, or RSUs, and (iii) PRSUs, and our diluted net income (loss) per share is the same as our basic net income (loss) per share.

Cash, Cash Equivalents, and R_2

Cash, Cash Equivalents, and Restricted Cash (Tables)	3 Months Ended
	Mar. 31, 2019
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]
Reconciliation of Components of Cash, Cash Equivalents, and Restricted Cash	The following table provides a reconciliation of the components of cash, cash equivalents and restricted cash reported in the accompanying condensed consolidated balance sheets to the total of the amount presented in the condensed consolidated statements of cash flows, in thousands: March 31, December 31, 2019 2018 Cash and cash equivalents $ 727,404 $ 161,037 Restricted cash included in other non-current assets 200 863 Total cash, cash equivalents and restricted cash presented in the condensed consolidated statement of cash flows $ 727,604 $ 161,900

Fair Value Disclosures (Tables)

Fair Value Disclosures (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Financial Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables present our valuation hierarchy for our financial assets and liabilities that are measured at fair value on a recurring basis, in thousands: Fair Value Measurements Using Balance Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) March 31, 2019: Assets: Money market funds(1) $ 656,849 $ 656,849 $ — $ — US government and government agency notes(2) 231,106 231,106 — — Corporate debt instruments(2) 317,158 — 317,158 — December 31, 2018: Assets: Money market funds(1) $ 62,438 $ 62,438 $ — $ — US government and government agency notes(2) 171,278 171,278 — — Corporate debt instruments(2) 240,481 — 240,481 — (1) Included in cash and cash equivalents in the accompanying (2) Included in either cash and cash equivalents or available-for-sale investments in the accompanying condensed consolidated balance sheets.

Investments, Available-for-Sa_2

Investments, Available-for-Sale (Tables)	3 Months Ended
	Mar. 31, 2019
Investments Debt And Equity Securities [Abstract]
Schedule of Investments, Available-for-Sale	I nvestments, available-for-sale, consisted of the following Maturity in years Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Estimated Fair Value March 31, 2019: US government and government agency notes < 1 $ 179,579 $ 40 $ (4 ) $ 179,615 Corporate debt securities < 1 197,167 145 (16 ) 197,296 Short-term investments, available-for-sale $ 376,746 $ 185 $ (20 ) $ 376,911 US government and government agency notes 1 – 5 $ 51,461 $ 33 $ (3 ) $ 51,491 Corporate debt securities 1 – 5 113,628 237 (2 ) 113,863 Investments, available-for-sale $ 165,089 $ 270 $ (5 ) $ 165,354 December 31, 2018: US government and government agency notes < 1 $ 139,274 $ — $ (18 ) $ 139,256 Corporate debt securities < 1 145,468 — (130 ) 145,338 Short-term investments, available-for-sale $ 284,742 $ — $ (148 ) $ 284,594 US government and government agency notes 1 – 5 $ 16,998 $ 6 $ — $ 17,004 Corporate debt securities 1 – 5 65,512 — (104 ) 65,408 Investments, available-for-sale $ 82,510 $ 6 $ (104 ) $ 82,412

Land, Property and Equipment (T

Land, Property and Equipment (Tables)	3 Months Ended
	Mar. 31, 2019
Property Plant And Equipment [Abstract]
Land, Property and Equipment	Land, property and equipment consisted of the following, in thousands: March 31, December 31, 2019 2018 Cost $ 70,637 $ 69,542 Less accumulated depreciation and amortization (47,192 ) (46,428 ) Land, property and equipment, net $ 23,445 $ 23,114

Accounts Payable and Other Ac_2

Accounts Payable and Other Accrued Liabilities (Tables)	3 Months Ended
	Mar. 31, 2019
Payables And Accruals [Abstract]
Accounts Payable and Other Accrued Liabilities	Accounts payable and other accrued liabilities consisted of the following, in thousands: March 31, December 31, 2019 2018 Accounts payable $ 1,643 $ 6,192 Accrued expenses 12,070 — Accrued compensation 3,700 8,622 Other accrued liabilities 2,735 1,367 Total accounts payable and other accrued liabilities $ 20,148 $ 16,181

Collaborations and License Ag_2

Collaborations and License Agreements (Tables)	3 Months Ended
	Mar. 31, 2019
Revenue From Contract With Customer [Abstract]
Summary of Revenue Disaggregated by Major Customers, Timing of Revenue Recognition and Revenue Classification	In the following table, revenue is disaggregated by major customers, timing of revenue recognition and revenue classification, in thousands. Three Months Ended March 31, 2019 2018 Customers United Therapeutics $ 800,000 $ — Eisai 823 2,228 Boehringer Ingelheim 84 460 Axovant — 568 Siegfried — 942 Other 150 64 Total $ 801,057 $ 4,262 Timing of revenue recognition Revenue recognized at a point in time $ 800,150 $ 1,755 Revenue recognized over time 907 2,507 Total $ 801,057 $ 4,262 Classification Revenue from continuing operations $ 801,057 $ 1,755 Revenue reported under discontinued operations — 2,507 Total $ 801,057 $ 4,262
Summary of Changes in Contract Assets	The following table provides detail of changes in our contract assets, in thousands: Contract Assets - Current Contract Assets - Non-Current Balances at December 31, 2018 $ 1,484 $ 4,471 Reductions of contract assets (18 ) (326 ) Balances at March 31, 2019 $ 1,466 $ 4,145

Share-based Compensation (Table

Share-based Compensation (Tables)	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share Based Compensation Expense	We recognized share-based compensation expense as follows, in thousands: Three months ended March 31, 2019 2018 Research and development $ 6,707 $ 1,650 General and administrative 6,317 2,383 Discontinued operations — 11 Total share-based compensation expense $ 13,024 $ 4,044
Summary of Stock Option Activity	The following table summarizes our stock option activity during the three months ended March 31, 2019, in thousands (except per share data): Options Weighted- Average Exercise Price Outstanding at January 1, 2019 6,541 $ 28.83 Granted 2,219 41.36 Exercised (125 ) 26.77 Forfeited/cancelled/expired (112 ) 28.70 Outstanding at March 31, 2019 8,523 $ 32.13

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Future Minimum Lease Payments	At March 31, 2019, the f uture lease payments under our existing financing obligations and non-cancellable operating leases were as follows, in thousands: Year ending December 31, Financing Obligations Operating Leases Remainder of 2019 $ 5,407 $ 812 2020 8,254 1,098 2021 8,461 976 2022 8,672 1,000 2023 8,889 1,025 2024 9,111 1,051 Thereafter 22,940 2,647 Total minimum lease payments 71,734 $ 8,609 Less amounts representing interest (24,735 ) Add amounts representing residual value 4,950 Lease financing obligations 51,949 Less current portion (3,410 ) $ 48,539 At December 31, 2018, the future minimum lease payments under our existing financing and operating lease obligations were as follows, in thousands: Year ending December 31, Financing Obligations Operating Leases 2019 $ 7,391 $ 1,050 2020 8,254 1,100 2021 8,461 976 2022 8,672 1,000 2023 8,889 1,025 Thereafter 32,052 3,698 Total minimum lease payments 73,719 $ 8,849 Less amounts representing interest (25,960 ) Add amounts representing residual value 4,950 Lease financing obligations 52,709 Less current portion (3,283 ) $ 49,426
Sublease Agreement
Expected Minimum Rental Payments to be Received under Sublease	At March 31, 2019, the expected minimum rental payments to be received under our subleases were as follows Year ending December 31, Remainder of 2019 $ 1,175 2020 1,873 2021 2,477 2022 3,487 2023 3,794 2024 3,896 Thereafter 9,839 Total $ 26,541

Income (Loss) Per Share (Tables

Income (Loss) Per Share (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Potentially Dilutive Securities Excluded from Calculation of Diluted Net Income (Loss) Per Share	The following table presents the weighted-average number of potentially dilutive securities that were excluded from our calculation of diluted net income (loss) per share, in thousands: Three months ended March 31, 2019 2018 Stock options 5,471 5,360 RSUs and unvested restricted stock — 25 Total 5,471 5,385

Basis of Presentation - Additio

Basis of Presentation - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)	Mar. 31, 2019USD ($)employee	Jan. 01, 2019USD ($)
Subsidiary Sale Of Stock [Line Items]
Loss from discontinued operations	$ (830)
Cash and cash equivalents and available-for-sale investments		$ 1,300,000
ASC 842
Subsidiary Sale Of Stock [Line Items]
Operating lease, liability			$ 6,300
Operating lease, right-of-use asset			$ 5,900
Siegfried
Subsidiary Sale Of Stock [Line Items]
Number of employees transferred | employee		50
Arena Gmb H
Subsidiary Sale Of Stock [Line Items]
Loss from discontinued operations	$ (800)

Cash, Cash Equivalents, and R_3

Cash, Cash Equivalents, and Restricted Cash - Reconciliation of Components of Cash, Cash Equivalents, and Restricted Cash (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 727,404	$ 161,037
Restricted cash included in other non-current assets	$ 200	$ 863
Restricted Cash, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Total cash, cash equivalents and restricted cash presented in the condensed consolidated statement of cash flows	$ 727,604	$ 161,900

Fair Value Disclosures - Financ

Fair Value Disclosures - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value Measurements, Recurring - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets:
Money market funds	$ 656,849	$ 62,438
US government and government agency notes	231,106	171,278
Corporate debt instruments	317,158	240,481
Quoted Prices in Active Markets (Level 1)
Assets:
Money market funds	656,849	62,438
US government and government agency notes	231,106	171,278
Significant Other Observable Inputs (Level 2)
Assets:
Corporate debt instruments	$ 317,158	$ 240,481

Investments, Available-for-Sa_3

Investments, Available-for-Sale - Schedule of Investments, Available-for-Sale (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Short-term investments, available-for-sale
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 376,746	$ 284,742
Gross Unrealized Gains	185
Gross Unrealized Losses	(20)	(148)
Estimated Fair Value	376,911	284,594
Short-term investments, available-for-sale | US government and government agency notes
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	179,579	139,274
Gross Unrealized Gains	40
Gross Unrealized Losses	(4)	(18)
Estimated Fair Value	179,615	139,256
Short-term investments, available-for-sale | Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	197,167	145,468
Gross Unrealized Gains	145
Gross Unrealized Losses	(16)	(130)
Estimated Fair Value	197,296	145,338
Investments, available-for-sale
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	165,089	82,510
Gross Unrealized Gains	270	6
Gross Unrealized Losses	(5)	(104)
Estimated Fair Value	165,354	82,412
Investments, available-for-sale | US government and government agency notes
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	51,461	16,998
Gross Unrealized Gains	33	6
Gross Unrealized Losses	(3)
Estimated Fair Value	$ 51,491	$ 17,004
Investments, available-for-sale | US government and government agency notes | Minimum
Schedule Of Available For Sale Securities [Line Items]
Maturity in years	1 year	1 year
Investments, available-for-sale | US government and government agency notes | Maximum
Schedule Of Available For Sale Securities [Line Items]
Maturity in years	5 years	5 years
Investments, available-for-sale | Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 113,628	$ 65,512
Gross Unrealized Gains	237
Gross Unrealized Losses	(2)	(104)
Estimated Fair Value	$ 113,863	$ 65,408
Investments, available-for-sale | Corporate debt securities | Minimum
Schedule Of Available For Sale Securities [Line Items]
Maturity in years	1 year	1 year
Investments, available-for-sale | Corporate debt securities | Maximum
Schedule Of Available For Sale Securities [Line Items]
Maturity in years	5 years	5 years

Land, Property and Equipment -

Land, Property and Equipment - Land, Property and Equipment (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Cost	$ 70,637	$ 69,542
Less accumulated depreciation and amortization	(47,192)	(46,428)
Land, property and equipment, net	$ 23,445	$ 23,114

Accounts Payable and Other Ac_3

Accounts Payable and Other Accrued Liabilities - Accounts Payable and Other Accrued Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accounts payable	$ 1,643	$ 6,192
Accrued expenses	12,070
Accrued compensation	3,700	8,622
Other accrued liabilities	2,735	1,367
Total accounts payable and other accrued liabilities	$ 20,148	$ 16,181

Collaborations and License Ag_3

Collaborations and License Agreements - Summary of Revenue Disaggregated by Major Customers, Timing of Revenue Recognition and Revenue Classification (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation Of Revenue [Line Items]
Revenue	$ 801,057	$ 4,262
Revenue from continuing operations	801,057	1,755
Revenue reported under discontinued operations		2,507
Revenue recognized at a point in time
Disaggregation Of Revenue [Line Items]
Revenue	800,150	1,755
Revenue recognized over time
Disaggregation Of Revenue [Line Items]
Revenue	907	2,507
United Therapeutics
Disaggregation Of Revenue [Line Items]
Revenue	800,000
Eisai
Disaggregation Of Revenue [Line Items]
Revenue	823	2,228
Boehringer Ingelheim
Disaggregation Of Revenue [Line Items]
Revenue	84	460
Axovant
Disaggregation Of Revenue [Line Items]
Revenue		568
Siegfried
Disaggregation Of Revenue [Line Items]
Revenue		942
Other
Disaggregation Of Revenue [Line Items]
Revenue	$ 150	$ 64

Collaborations and License Ag_4

Collaborations and License Agreements - Summary of Changes in Contract Assets (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Change In Contract With Customer Asset [Abstract]
Contract Assets - Current, Beginning balance	$ 1,484
Contract Assets - Current, Reductions of contract assets	(18)
Contract Assets - Current, Ending balance	1,466
Contract Assets - Non-Current, Beginning balance	4,471
Contract Assets - Non-Current, Reductions of contract assets	(326)
Contract Assets - Non-Current, Ending balance	$ 4,145

Collaborations and License Ag_5

Collaborations and License Agreements - Additional Information (Detail)	Jan. 24, 2019USD ($)	Mar. 31, 2019USD ($)	Mar. 31, 2018USD ($)	Mar. 31, 2018CHF (SFr)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction costs		$ 14,573,000
License agreement costs incurred related to transaction fees		14,573,000
Revenues		801,057,000	$ 1,755,000
Lorcaserin Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues		250,000,000
Royalty Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues		973,000	727,000
Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement		$ 25,000,000
Eisai | 9.5% Royalty Rate
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty rate on annual net sales		9.50%
Eisai | 13.5% Royalty Rate
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty rate on annual net sales		13.50%
Eisai | 18.5% Royalty Rate
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty rate on annual net sales		18.50%
Maximum | Eisai | 9.5% Royalty Rate
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty portion of annual net sales amount		$ 175,000,000
Maximum | Eisai | 13.5% Royalty Rate
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty portion of annual net sales amount		500,000,000
Minimum | Eisai | 13.5% Royalty Rate
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty portion of annual net sales amount		175,000,000
Minimum | Eisai | 18.5% Royalty Rate
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty portion of annual net sales amount		500,000,000
Eisai Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional manufacturing support payments received | SFr				SFr 8,700,000
Eisai Agreement | Royalty Revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues		800,000	700,000
Supply Agreement | Product Sales
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues		$ 0	$ 1,500,000
United Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement right description		In November 2018, we entered into an exclusive license agreement, or the United Therapeutics Agreement, with United Therapeutics. Under the United Therapeutics Agreement, we granted United Therapeutics an exclusive, worldwide, royalty-bearing license to develop, manufacture and commercialize ralinepag in any formulation. This transaction was completed on January 24, 2019.
Collaborative agreement completion date	Jan. 24, 2019
Transaction costs	$ 17,000,000	$ 14,600,000
License agreement costs incurred related to transaction fees	$ 17,000,000	14,600,000
Collaborative agreement upfront payments		800,000,000
United Therapeutics | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement		400,000,000
United Therapeutics | Non U.S. Market
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement		150,000,000
United Therapeutics | U.S. Market
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional milestone payments on achievement		$ 250,000,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Income Tax Disclosure [Abstract]
Income tax expense	$ 110,333

Share-based Compensation - Shar

Share-based Compensation - Share Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 13,024	$ 4,044
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	6,707	1,650
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 6,317	2,383
Discontinued operations
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense		$ 11

Share-based Compensation - Summ

Share-based Compensation - Summary of Stock Option Activity (Detail) - Stock options shares in Thousands	3 Months Ended
	Mar. 31, 2019$ / sharesshares
Number of stock options
Outstanding at January 1, 2019 | shares	6,541
Granted | shares	2,219
Exercised | shares	(125)
Forfeited/cancelled/expired | shares	(112)
Outstanding at March 31, 2019 | shares	8,523
Weighted Average Exercise Price ($ per share)
Outstanding at January 1, 2019 | $ / shares	$ 28.83
Granted | $ / shares	41.36
Exercised | $ / shares	26.77
Forfeited/cancelled/expired | $ / shares	28.70
Outstanding at March 31, 2019 | $ / shares	$ 32.13

Share-based Compensation - Addi

Share-based Compensation - Additional Information (Detail) - Performance restricted stock units - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units granted (shares)		297,000
Vesting period	3 years	3 years
Threshold consecutive trading days		5 days
Threshold non-consecutive trading days		10 days
PRSU grant-date fair value		$ 18.1
Compensation expense of requisite service period		1 year 2 months 12 days
Shares issued			32,322
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares to be awarded as a percentage of target amounts		200.00%
Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock closing price ($ per share)		$ 60
Common stock closing price, percentage		50.00%
Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock closing price ($ per share)		$ 67.50
Common stock closing price, percentage		100.00%
Tranche Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock closing price ($ per share)		$ 75
Common stock closing price, percentage		200.00%

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019USD ($)ft²Property	Mar. 31, 2018USD ($)	Dec. 31, 2017Property	Dec. 31, 2016Property	Jan. 01, 2019USD ($)	Dec. 31, 2018USD ($)
Operating Leased Assets [Line Items]
Number of properties under sale and leaseback agreements | Property	3
Sale and leaseback transaction, interest expense	$ 1,200	$ 1,500
Less amounts representing interest	$ 24,735					$ 25,960
Sale leaseback transaction, description	Through the remaining terms of the leases until their expiration in May 2027
Add amounts representing residual value	$ 4,950					$ 4,950
Rent expense	300	400
Rent income from subleases	$ 700	$ 600
Beacon Discovery, Inc.
Operating Leased Assets [Line Items]
Number of properties subleased | Property			1	1
Sublease expiration period			2027-05	2027-05
ASC 842
Operating Leased Assets [Line Items]
Operating lease, liability					$ 6,300
Operating lease, right-of-use asset					$ 5,900
Weighted average discount rate	7.25%
Properties under sale and leaseback agreements
Operating Leased Assets [Line Items]
Percentage of annual increase in monthly rental payments	2.50%
Properties under operating lease | San Diego, California
Operating Leased Assets [Line Items]
Percentage of annual increase in monthly rental payments	2.50%
Operating lease agreement expiration date	2027-05
Operating lease, right-of-use asset	$ 5,800
Operating lease, right-of-use asset, statement of financial position [extensible list]	us-gaap:OtherAssetsNoncurrent
Operating lease, liability, current	$ 500
Operating lease, liability, current, statement of financial position [extensible list]	us-gaap:AccountsPayableAndOtherAccruedLiabilitiesCurrent
Operating lease, liability, noncurrent	$ 5,700
Operating lease, liability, noncurrent, statement of financial position [extensible list]	us-gaap:OtherLiabilitiesNoncurrent
Properties under operating lease | Zug, Switzerland
Operating Leased Assets [Line Items]
Operating lease agreement expiration date	2020-09
Area of office space | ft²	10,500
Additional office space, lease inception date	Jun. 1, 2019

Leases - Future Minimum Lease P

Leases - Future Minimum Lease Payments (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Financing Obligations
Remainder of 2019	$ 5,407
2020	8,254
2021	8,461
2022	8,672
2023	8,889
2024	9,111
Thereafter	22,940
Total minimum lease payments	71,734
Less amounts representing interest	(24,735)	$ (25,960)
Add amounts representing residual value	4,950	4,950
Lease financing obligations	51,949	52,709
Current portion of lease financing obligations	(3,410)	(3,283)
Lease financing obligations, less current portion	48,539	49,426
Operating Leases
Remainder of 2019	812
2020	1,098
2021	976
2022	1,000
2023	1,025
2024	1,051
Thereafter	2,647
Total minimum lease payments	$ 8,609
Financing Obligations
2019		7,391
2020		8,254
2021		8,461
2022		8,672
2023		8,889
Thereafter		32,052
Total minimum lease payments		73,719
Operating Leases
2019		1,050
2020		1,100
2021		976
2022		1,000
2023		1,025
Thereafter		3,698
Total minimum lease payments		$ 8,849

Leases - Expected Minimum Renta

Leases - Expected Minimum Rental Payments to be Received under Sublease (Detail) - Sublease Agreement $ in Thousands	Mar. 31, 2019USD ($)
Operating Leased Assets [Line Items]
Remainder of 2019	$ 1,175
2020	1,873
2021	2,477
2022	3,487
2023	3,794
2024	3,896
Thereafter	9,839
Total	$ 26,541

Income (Loss) Per Share - Poten

Income (Loss) Per Share - Potentially Dilutive Securities Excluded from Calculation of Diluted Net Income (Loss) Per Share (Detail) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities excluded from calculation of diluted net loss per share (shares)	5,471	5,385
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities excluded from calculation of diluted net loss per share (shares)	5,471	5,360
RSUs and unvested restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities excluded from calculation of diluted net loss per share (shares)		25