Arena Pharmaceuticals (ARNA) 10-Q 7 Aug 15 2015 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2015	Aug. 04, 2015
Document And Entity Information [Abstract]
Entity Registrant Name	ARENA PHARMACEUTICALS INC
Trading Symbol	ARNA
Entity Central Index Key	1,080,709
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Jun. 30, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		242,241,710

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	[1]
Current assets:
Cash and cash equivalents	$ 216,701	$ 163,209
Accounts receivable	4,194	3,712
Inventory	11,001	10,831
Prepaid expenses and other current assets	4,074	4,144
Total current assets	235,970	181,896
Land, property and equipment, net	81,412	82,919
Intangibles, net	8,660	8,482
Other non-current assets	3,081	3,088
Total assets	329,123	276,385
Current liabilities:
Accounts payable and other accrued liabilities	8,215	10,209
Accrued clinical and preclinical study fees	4,333	7,027
Payable to Eisai	10,031	23,705
Payable to Siegfried for acquisition of land and building	8,793	8,217
Current portion of deferred revenues	26,917	15,238
Derivative liabilities	852	474
Current portion of lease financing obligations	2,729	2,492
Total current liabilities	61,870	67,362
Deferred rent	423	369
Deferred revenues, less current portion	92,648	93,064
Lease financing obligations, less current portion	$ 66,824	$ 68,245
Commitments and contingencies
Stockholders’ equity:
Common stock	$ 24	$ 22
Additional paid-in capital	1,423,387	1,312,656
Accumulated other comprehensive income	3,290	2,908
Accumulated deficit	(1,319,343)	(1,268,241)
Total stockholders’ equity	107,358	47,345
Total liabilities and stockholders’ equity	$ 329,123	$ 276,385
[1]	The balance sheet data at December 31, 2014, has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by US generally accepted accounting principles for complete financial statements.

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues:
Net product sales	$ 4,285	$ 3,529	$ 10,903	$ 6,411
Toll manufacturing	1,390	578	1,736	1,026
Total revenues	9,181	12,801	21,437	19,615
Operating Costs and Expenses:
Cost of product sales	1,303	1,463	4,494	2,294
Cost of toll manufacturing	1,812	547	2,214	1,043
Research and development	24,201	27,025	46,169	48,013
General and administrative	8,844	9,132	17,283	17,169
Total operating costs and expenses	36,160	38,167	70,160	68,519
Loss from operations	(26,979)	(25,366)	(48,723)	(48,904)
Interest and Other Income (Expense):
Interest income	34	24	68	53
Interest expense	(1,754)	(1,735)	(3,450)	(3,482)
Gain (loss) from valuation of derivative liabilities	1,171	1,006	(378)	896
Gain on sale of available-for-sale securities	0	33,277	0	33,277
Other	721	274	1,381	385
Total interest and other income (expense), net	172	32,846	(2,379)	31,129
Net income (loss)	$ (26,807)	$ 7,480	$ (51,102)	$ (17,775)
Net income (loss) per share:
Basic, in dollars per share	$ (0.11)	$ 0.03	$ (0.21)	$ (0.08)
Diluted, in dollars per share	$ (0.11)	$ 0.03	$ (0.21)	$ (0.08)
Shares used in calculating net income (loss) per share:
Basic, in shares	242,067	219,682	238,903	219,453
Diluted, in shares	242,067	225,341	238,903	219,453
Comprehensive Income (Loss):
Net income (loss)	$ (26,807)	$ 7,480	$ (51,102)	$ (17,775)
Foreign currency translation gain (loss)	527	(484)	382	(393)
Reclassification adjustment for realized gain on sale of available-for-sale securities	0	(33,277)	0	(33,277)
Unrealized holding gain (loss) on available-for-sale securities	0	(1,644)	0	51,590
Comprehensive income (loss)	(26,280)	(27,925)	(50,720)	145
Eisai
Revenues:
Net product sales	3,893	3,529	8,329	6,411
Other collaborative revenue	3,213	8,554	5,349	11,901
Total revenues	7,106	12,083	13,678	18,312
Other
Revenues:
Other collaborative revenue	$ 293	$ 140	$ 3,449	$ 277

Condensed Consolidated Stateme4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015		Jun. 30, 2014
Operating Activities
Net income (loss)	$ (51,102)		$ (17,775)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	4,949		4,201
Amortization of intangibles	90		289
Share-based compensation	7,947		6,543
(Gain) loss from valuation of derivative liabilities	378		(896)
Gain on sale of available-for-sale securities	0		(33,277)
Amortization of prepaid financing costs	68		68
Gain on sale of equipment	0		(47)
Changes in assets and liabilities:
Accounts receivable	(412)		3,187
Inventory	807		329
Prepaid expenses and other assets	768		(1,115)
Payables and accrued liabilities	(20,894)		(4,570)
Deferred revenues	10,367		(10,037)
Deferred rent	54		65
Net cash used in operating activities	(46,980)		(53,035)
Investing Activities
Proceeds from sale of available-for-sale securities	0		33,277
Purchases of property and equipment	(1,769)		(4,419)
Proceeds from sale of equipment	0		47
Other non-current assets	(55)		209
Net cash provided by (used in) investing activities	(1,824)		29,114
Financing Activities
Principal payments on lease financing obligations	(1,184)		(973)
Proceeds from issuance of common stock	102,663		4,258
Net cash provided by financing activities	101,479		3,285
Effect of exchange rate changes on cash	817		(444)
Net increase (decrease) in cash and cash equivalents	53,492		(21,080)
Cash and cash equivalents at beginning of period	163,209	[1]	221,878
Cash and cash equivalents at end of period	$ 216,701		$ 200,798
[1]	The balance sheet data at December 31, 2014, has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by US generally accepted accounting principles for complete financial statements.

Basis of Presentation

Basis of Presentation	6 Months Ended
	Jun. 30, 2015
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements of Arena Pharmaceuticals, Inc., which include our wholly owned subsidiaries, 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, 2014, as filed with the Securities and Exchange Commission, or SEC, from which we derived our balance sheet as of December 31, 2014. The accompanying 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 financial statements do not include all of the information and notes required by GAAP for complete financial statements. The accompanying 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. In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2014-09, “Revenue from Contracts with Customers.” ASU No. 2014-09 outlines a comprehensive revenue recognition model which will supersede most current revenue recognition guidance. ASU No. 2014-09 is effective for annual reporting periods, and interim periods within those periods, beginning after December 15, 2017. ASU No. 2014-09 allows for two methods of adoption: (a) “full retrospective” adoption, meaning the standard is applied to all periods presented, or (b) “modified retrospective” adoption, meaning the cumulative effect of applying ASU No. 2014-09 is recognized as an adjustment to the opening retained earnings balance for the year of implementation. We have not yet selected an adoption method as we are currently evaluating the impact of ASU No. 2014-09 on our consolidated financial statements. In August 2014, the FASB issued ASU No. 2014-15, “Presentation of Financial Statements – Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern.” Under GAAP, continuation of a reporting entity as a going concern is presumed as the basis for preparing financial statements unless and until the entity’s liquidation becomes imminent. Preparation of financial statements under this presumption is commonly referred to as the going concern basis of accounting. If and when an entity’s liquidation becomes imminent, financial statements should be prepared under the liquidation basis of accounting. Even when an entity’s liquidation is not imminent, there may be conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern. In those situations, financial statements should continue to be prepared under the going concern basis of accounting, but ASU No. 2014-15 should be followed to determine whether to disclose information about any relevant conditions and events. ASU No. 2014-15 is effective for the annual reporting period ending after December 15, 2016, and for annual and interim periods thereafter. We do not expect the adoption of ASU No. 2014-15 to have a material impact on our consolidated financial statements. 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.

Fair Value Disclosures

Fair Value Disclosures	6 Months Ended
	Jun. 30, 2015
Fair Value Disclosures [Abstract]
Fair Value Disclosures	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 at June 30, 2015 Balance Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds 1 $ 154,989 $ 154,989 $ 0 $ 0 Liabilities: Warrant derivative liabilities $ 852 $ 0 $ 852 $ 0 Fair Value Measurements at December 31, 2014 Balance Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds 1 $ 143,913 $ 143,913 $ 0 $ 0 Liabilities: Warrant derivative liabilities $ 474 $ 0 $ 474 $ 0 ______________________ (1) Included in cash and cash equivalents on our condensed consolidated balance sheets.

Inventory

Inventory	6 Months Ended
	Jun. 30, 2015
Inventory Disclosure [Abstract]
Inventory	Inventory Inventory consisted of the following, in thousands: June 30, 2015 December 31, 2014 Raw materials $ 2,470 $ 1,167 Work in process 3,748 3,520 Finished goods at Arena GmbH 7 3,681 Finished goods at Eisai 4,112 2,463 Finished goods at Ildong 664 0 Total inventory $ 11,001 $ 10,831

Land, Property and Equipment

Land, Property and Equipment	6 Months Ended
	Jun. 30, 2015
Property, Plant and Equipment [Abstract]
Land, Property and Equipment	Land, Property and Equipment Land, property and equipment consisted of the following, in thousands: June 30, 2015 December 31, 2014 Cost $ 179,157 $ 174,938 Less accumulated depreciation and amortization (97,745 ) (92,019 ) Land, property and equipment, net $ 81,412 $ 82,919

Accounts Payable and Other Accr

Accounts Payable and Other Accrued Liabilities	6 Months Ended
	Jun. 30, 2015
Payables and Accruals [Abstract]
Accounts Payable and Other Accrued Liabilities	Accounts Payable and Other Accrued Liabilities Accounts payable and other accrued liabilities consisted of the following, in thousands: June 30, 2015 December 31, 2014 Accounts payable $ 2,662 $ 2,844 Accrued compensation 4,409 4,792 Other accrued liabilities 1,144 2,573 Total accounts payable and other accrued liabilities $ 8,215 $ 10,209

Derivative Liabilities

Derivative Liabilities	6 Months Ended
	Jun. 30, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Liabilities	Derivative Liabilities In August 2008, we issued a warrant to purchase 1,106,344 shares of our common stock at an exercise price of $7.71 per share that expires on August 14, 2015. As a result of the warrant’s anti-dilution provision and certain of our subsequent equity issuances at prices below the adjustment price of $6.72 defined in the warrant agreement, the number of shares issuable upon exercise of the warrant increased and the exercise price decreased. At June 30, 2015, the number of shares issuable upon exercise of the outstanding warrant was 1,965,418 at an exercise price of $4.34 per share. The outstanding warrant, which was valued at $0.9 million and $0.5 million at June 30, 2015, and December 31, 2014, respectively, is recorded as a current derivative liability on our condensed consolidated balance sheets. Our outstanding warrant was revalued on each balance sheet date, with changes in the fair value between reporting periods recorded in the interest and other income (expense) section of our condensed consolidated statements of operations and comprehensive income (loss).

Marketing and Supply Agreement

Marketing and Supply Agreement with Eisai	6 Months Ended
	Jun. 30, 2015
Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Marketing and Supply Agreement with Eisai/Ildong	Marketing and Supply Agreement with Eisai In November 2013, our wholly owned subsidiary, Arena Pharmaceuticals GmbH, or Arena GmbH, and Eisai Inc. and Eisai Co., Ltd. (collectively with Eisai Inc., Eisai) entered into the Second Amended and Restated Marketing and Supply Agreement, or Eisai Agreement. The Eisai Agreement amended and restated the previous agreement and expanded Eisai’s exclusive commercialization rights for lorcaserin to all of the countries in the world, except for South Korea, Taiwan, Australia, New Zealand and Israel. Lorcaserin is approved in the United States for chronic weight management in adults who are overweight with a comorbidity or obese, and was made available to patients by prescription in the United States by Eisai in June 2013. In addition to providing commercialization rights, which are subject to applicable regulatory approval, we manufacture and sell lorcaserin to Eisai and provide Eisai with services related to development and regulatory activities. Under the Eisai Agreement, we have received an upfront payment and payments from sales of lorcaserin, and are entitled to receive payments from future sales of lorcaserin, milestone payments based on the achievement of regulatory filings and approvals, one-time purchase price adjustment payments and other payments. Prior to entering into the Eisai Agreement, Arena GmbH and Eisai Inc. entered into the original marketing and supply agreement in July 2010, under which we granted Eisai Inc. exclusive commercialization rights for lorcaserin solely in the United States and its territories and possessions. In May 2012, Arena GmbH and Eisai Inc. amended and restated such agreement by entering into the first amended agreement, which expanded Eisai Inc.’s exclusive commercialization rights to include most of North and South America. The following table summarizes the revenues we recognized under our collaboration with Eisai for the periods presented, in thousands: Three months ended Six months ended 2015 2014 2015 2014 Net product sales $ 3,893 $ 3,529 $ 8,329 $ 6,411 Amortization of upfront payments 1,885 1,885 3,770 3,860 Reimbursement of development expenses 1,156 6,568 1,347 7,313 Milestone payment 0 0 0 500 Reimbursement of patent and trademark expenses 172 101 232 228 Subtotal other Eisai collaborative revenue 3,213 8,554 5,349 11,901 Total $ 7,106 $ 12,083 $ 13,678 $ 18,312 The following table summarizes the deferred revenues under our collaboration with Eisai, in thousands: June 30, 2015 December 31, 2014 Upfront payments $ 90,704 $ 94,474 Net product sales 16,833 7,081 Total deferred revenues attributable to Eisai 107,537 101,555 Less current portion (24,374 ) (14,622 ) Deferred revenues attributable to Eisai, less current portion $ 83,163 $ 86,933 Upfront and Milestone Payments. In connection with entering into the Eisai Agreement, we received from Eisai an upfront payment of $60.0 million . This payment is in addition to the $50.0 million and $5.0 million in upfront payments we received from Eisai in connection with entering into the original agreement and the first amended agreement, respectively. Revenues from these upfront payments were deferred, as we determined that the exclusive rights did not have standalone value without our ongoing development and regulatory activities. Accordingly, these payments are recognized ratably as revenue over the periods in which we expect the services to be rendered, which are approximately 15 years for the Eisai Agreement and first amended agreement and 16 years for the original agreement. In addition to the upfront payments, we have received from Eisai a total of $86.5 million in milestones payments, and we are eligible to receive up to an aggregate of $176.0 million in additional regulatory and development milestone payments. Product Purchase Price and Purchase Price Adjustment Payments. We manufacture lorcaserin at our facility in Switzerland, and sell lorcaserin to Eisai for Eisai’s commercialization in the United States and, subject to applicable regulatory approval, in the other territories under the Eisai Agreement (other than Europe, China and Japan) for a purchase price starting at 31.5% and 30.75% , respectively (and starting at 27.5% in Europe, China and Japan), of Eisai’s aggregate annual net product sales (which are the gross invoiced sales less certain deductions described in the Eisai Agreement), or the Eisai Product Purchase Price, in the respective territory. The Eisai Product Purchase Price will increase on a tiered basis in the United States and the other territories (other than Europe, China and Japan) to as high as 36.5% and 35.75% , respectively, on the portion of Eisai’s annual aggregate net product sales exceeding $750.0 million in all territories other than Europe, China and Japan. The Eisai Product Purchase Price will increase to 35% in Europe, China and Japan on the portion of Eisai’s annual aggregate net product sales exceeding $500.0 million in such territories. The Eisai Product Purchase Price is subject to reduction (for sales in a particular country), including in the event of generic competition in the applicable country. The revenue we recognize for BELVIQ product revenue related to the use of vouchers and product samples is based on our cost of goods sold. In addition to payments for purchases of lorcaserin, we are eligible to receive up to an aggregate of $1.56 billion in one-time purchase price adjustment payments and other payments. These payments include up to an aggregate of $1.19 billion that are based on Eisai’s annual net product sales of lorcaserin in all of the territories under the Eisai Agreement on an aggregate basis, with the first and last amounts payable with annual net product sales of $250.0 million and $2.5 billion , respectively. Of these payments, Eisai will pay us a total of $330.0 million for annual net product sales of up to $1.0 billion . The $1.56 billion also includes $370.0 million in one-time purchase price adjustment payments we are eligible to receive based on annual net product sales in the non-US territories, comprised of $185.0 million based on Eisai’s annual net product sales in the non-US territories in North and South America and $185.0 million based on Eisai’s annual net product sales in the territories outside of North and South America. The first and last amounts are payable upon first achievement of annual net product sales of $100.0 million and $1.0 billion , respectively, with respect to each of the following areas: (i) the non-US territories in North and South America and (ii) the territories outside of North and South America. In addition, we are also eligible to receive certain payments by Eisai if certain annual minimum sales requirements in Mexico, Canada and Brazil are not met during the first ten years after initial commercial sale in such territories. The amount that Eisai pays us for lorcaserin product supply is based on Eisai’s estimated price at the time the order is shipped, which is Eisai’s estimate of the Eisai Product Purchase Price, and is subject to change on April 1 and October 1 of each year. Eisai’s estimate of the Eisai Product Purchase Price was changed as of October 1, 2013, and there was no further change as of April 1, 2014, October 1, 2014, or April 1, 2015. At the end of Eisai’s fiscal year (March 31), the estimated price paid to us for product that Eisai sold to their distributors is compared to the Eisai Product Purchase Price of such product, and the difference is either refunded back to Eisai (for overpayments) or paid to us (for underpayments). On a monthly basis, Eisai provides us the total amount of net product sales for the month, details of the total deductions from gross to net product sales and the sales in units. We recognize our revenues monthly based on our percentage of Eisai’s monthly net product sales figures. When the revenues we recognize differ from the estimated price that Eisai paid us for such product, the difference is reclassified from deferred revenues to a receivable or payable account, as appropriate. We also adjust the deferred revenues balance for the product supply held at Eisai based on the most current net product sales figures provided to us, with the difference reclassified from deferred revenues to a receivable or payable account. In the three months ended June 30, 2015 , we recognized revenues from our portion of Eisai net product sales of BELVIQ of $3.9 million , of which $3.8 million related to sales at the Eisai Product Purchase Price and $0.1 million related to redemptions of vouchers. In the six months ended June 30, 2015 , we recognized revenues from our portion of Eisai net product sales of BELVIQ of $8.3 million , of which $7.8 million related to sales at the Eisai Product Purchase Price and $0.5 million related to redemptions of vouchers. The Eisai Product Purchase Price for the product Eisai has sold to date was lower than the initial estimated price that Eisai paid us for such product, primarily because (i) the price that Eisai paid us did not include deductions for the use of vouchers and savings cards or for certain items related to product launch and (ii) the subsequent allocation of certain bottles of BELVIQ for product sampling initiated by Eisai as part of its commercialization efforts. In January 2015, Eisai announced the launch of a new savings card which enables eligible patients without commercial coverage for BELVIQ to pay no more than $75 for each monthly prescription while those patients with commercial coverage for BELVIQ are able to use the card to obtain additional savings if their copay is greater than $50 per monthly prescription. The new savings card is subject to certain restrictions, including the exclusion of patients who are eligible for state or federal healthcare programs. These excess payments, which total the $10.0 million classified as Payable to Eisai on our condensed consolidated balance sheet at June 30, 2015 , are primarily related to the above deductions, product sampling and the January 2015 launch of the new savings card. On a quarterly basis, subsequent to the end of each calendar quarter, we refund to Eisai the portion of these excess payments related to product sampling for product shipped to physicians during the quarter. On an annual basis, subsequent to the end of Eisai’s fiscal year, we refund to Eisai the portion of these excess payments related to product sold by Eisai to their distributors through March 31. Development Payments. In connection with the US approval of BELVIQ, the US Food and Drug Administration, or FDA, is requiring (i) an evaluation as part of the cardiovascular outcomes trial, or CVOT, of the effect of long-term treatment with BELVIQ on the incidence of major adverse cardiovascular events, or MACE, in overweight and obese patients with cardiovascular disease or multiple cardiovascular risk factors and (ii) the conduct of postmarketing studies to assess the safety and efficacy of BELVIQ for weight management in obese pediatric and adolescent patients. In addition to the FDA-required studies, we and Eisai initially prioritized the development areas of a once-daily formulation, smoking cessation, co-administration with phentermine, as well as potentially exploring, including as part of the CVOT, BELVIQ’s effect on conversion to type 2 diabetes and improvements in cardiovascular outcomes. The chart below summarizes the general agreement regarding cost sharing between Eisai and us for significant development activities under the Eisai Agreement. In addition, Eisai or we may from time to time conduct approved development of lorcaserin at such party’s own expense. Eisai Second Amended and Restated Marketing and Supply Agreement: Cost Sharing for Development United States Rest of North and South America Remaining Territories BELVIQ - Pre-approval* Not Applicable General Eisai: 90%; Arena: 10% Certain stability work Eisai: 50%; Arena: 50% Up to a total of $100.0 million - Eisai: 50%; Arena: 50% Thereafter, Eisai: 100% BELVIQ - Post-approval* General Eisai: 90%; Arena 10% Non-FDA required portion of CVOT Up to $80.0 million - Eisai: 50%; Arena: 50% Thereafter, Eisai: 100% Certain pediatric studies Eisai: 50%; Arena: 50% General Eisai: 90%; Arena: 10% Certain stability work Eisai: 50%; Arena: 50% Up to a total of $50.0 million - Eisai: 50%; Arena: 50% Thereafter, Eisai: 90%; Arena: 10% Lorcaserin products other than BELVIQ - Pre-approval Up to a total of $250.0 million (as reduced by up to $80.0 million for non-FDA required portion of CVOT) -Eisai: 50%; Arena: 50% Lorcaserin products other than BELVIQ - Post-approval Up to a total of $100.0 million in the aggregate across all additional products - Eisai: 50%; Arena: 50% Thereafter, Eisai: 90%; Arena: 10% ______________________ * Development required by a regulatory authority, with the exception of the non-FDA required portions of the CVOT. Certain Other Terms. Please refer to our Annual Report on Form 10-K for the year ended December 31, 2014 , for additional information regarding termination, indemnification, product liability, certain limitations and other provisions included in the Eisai Agreement.

Marketing and Supply Agreemen12

Marketing and Supply Agreement with Ildong	6 Months Ended
	Jun. 30, 2015
Ildong
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Marketing and Supply Agreement with Eisai/Ildong	Marketing and Supply Agreement with Ildong In November 2012, Arena GmbH and Ildong Pharmaceutical Co., Ltd., or Ildong, entered into the Marketing and Supply Agreement, or Ildong Agreement. Under this agreement, we granted Ildong exclusive rights to commercialize BELVIQ in South Korea for weight loss or weight management in obese and overweight patients. We also provide certain services and will manufacture and sell BELVIQ to Ildong. Ildong has agreed not to conduct activities outside of our agreement related to the approval or commercialization of any other pharmaceutical product for weight loss, weight management or obesity in South Korea, with the exception of phentermine. In connection with entering into the Ildong Agreement, we received from Ildong an upfront payment of $5.0 million , less withholding taxes. Revenues from this upfront payment were deferred, as we determined that the exclusive rights did not have standalone value without our ongoing development and regulatory activities. Accordingly, this payment is recognized ratably as revenue over the period in which we expect the services to be rendered, which is approximately 14 years. In addition to the upfront payment, we received a milestone payment of $3.0 million , less withholding taxes, in March 2015, which we earned upon the February 2015 approval of BELVIQ for marketing in South Korea for weight management. We manufacture BELVIQ at our facility in Switzerland, and sell BELVIQ to Ildong for a purchase price starting at the higher of the defined minimum amount or 35% of Ildong’s annual net product sales (which are the gross invoiced sales less certain deductions described in the Ildong Agreement), or the Ildong Product Purchase Price. The Ildong Product Purchase Price will increase on a tiered basis up to the higher of the defined minimum amount or 45% on the portion of annual net product sales exceeding $15.0 million . However, in no event will the Ildong Product Purchase Price be less than a defined minimum amount adjusted annually based on a consumer price index. For the three and six months ended June 30, 2015 , the Ildong Product Purchase Price equaled the defined minimum amount (which exceeded the 45% tier). If certain annual net product sales amounts are not met, we can convert Ildong’s right to commercialize BELVIQ in South Korea to be non-exclusive. We recognized revenues from our portion of Ildong net product sales of BELVIQ of $0.4 million and $2.6 million for the three and six months ended June 30, 2015 , respectively.

Share-based Activity

Share-based Activity	6 Months Ended
	Jun. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Activity	Share-based Activity Share-based Compensation . We recognized share-based compensation expense as follows, in thousands: Three months ended Six months ended 2015 2014 2015 2014 Research and development $ 2,185 $ 1,742 $ 4,241 $ 3,523 General and administrative 1,929 1,600 3,706 3,020 Total share-based compensation expense $ 4,114 $ 3,342 $ 7,947 $ 6,543 Total share-based compensation expense capitalized into inventory $ 43 $ 39 $ 105 $ 39 Share-based Award Activity. The following table summarizes our stock option activity during the six months ended June 30, 2015 , in thousands (except per share data): Options Weighted- Average Exercise Price Outstanding at January 1, 2015 15,831 $ 5.25 Granted 3,037 4.47 Exercised (745 ) 2.06 Forfeited/cancelled/expired (565 ) 6.33 Outstanding at June 30, 2015 17,558 $ 5.21 The following table summarizes activity with respect to our time-based restricted stock unit awards, or RSUs, during the six months ended June 30, 2015 , in thousands (except per share data): RSUs Weighted- Average Grant-Date Fair Value Unvested at January 1, 2015 456 $ 5.72 Granted 281 4.11 Vested (88 ) 6.50 Forfeited/cancelled 0 Unvested at June 30, 2015 649 $ 4.92 In March 2015, we granted our executive officers Total Stockholder Return, or TSR, performance restricted stock unit, or PRSU, awards. The PRSUs may be earned and converted into outstanding shares of our common stock based on the TSR of our common stock relative to the TSR over a three-year performance period beginning March 1, 2015, of the NASDAQ Biotechnology Index. In the aggregate, the target number of shares of common stock that may be earned under the PRSUs granted in March 2015 is 745,000 ; however, the actual number of shares that may be earned ranges from 0% to 200% of such amount. In addition, there is a cap on the number of shares that can be earned under the PRSUs equal to six times the grant-date fair value of each award, and funding is capped at 100% if the absolute 3 -year TSR is negative even if performance is above the median. As these awards contain a market condition, we used a Monte Carlo simulation model to estimate the grant-date fair value, which totaled $3.4 million and which is being recognized over the performance period. The following table sets forth the assumptions used to value the PRSUs granted in March 2015 and their estimated grant-date fair value: Risk-free interest rate 1.1 % Dividend yield 0 % Expected volatility 75 % Remaining performance period (years) 2.97 Estimated fair value per share of PRSUs granted $ 4.50 The aggregate intrinsic value of all of the outstanding PRSUs granted to date at June 30, 2015 , was $10.3 million . All of the PRSUs granted to date were outstanding and unvested at June 30, 2015 .

Concentrations of Credit Risk a

Concentrations of Credit Risk and Major Customers	6 Months Ended
	Jun. 30, 2015
Risks and Uncertainties [Abstract]
Concentrations of Credit Risk and Major Customers	Concentrations of Credit Risk and Major Customers Financial instruments, which potentially subject us to concentrations of credit risk, consist primarily of cash and cash equivalents. 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 and government-sponsored enterprise obligations and in corporate debt instruments that are rated investment grade, in accordance with an investment policy approved by our Board of Directors. Eisai and Ildong are the exclusive distributors of BELVIQ in the United States and South Korea, respectively, which are the only jurisdictions for which BELVIQ has received regulatory approval for marketing. We also produce drug products for Siegfried AG, or Siegfried, under a toll manufacturing agreement, and most of our toll manufacturing revenues are attributable to Siegfried. Percentages of our total revenues are as follows: Three months ended Six months ended 2015 2014 2015 2014 Eisai Agreement 77.4 % 94.4 % 63.8 % 93.4 % Ildong Agreement 5.3 % 0.7 % 26.9 % 0.9 % Toll manufacturing agreements 15.2 % 4.5 % 8.1 % 5.2 % Other collaborative agreements 2.1 % 0.4 % 1.2 % 0.5 % Total percentage of revenues 100.0 % 100.0 % 100.0 % 100.0 %

Net Income (Loss) Per Share

Net Income (Loss) Per Share	6 Months Ended
	Jun. 30, 2015
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	Net Income (Loss) Per Share We calculate basic and diluted net loss per share using the weighted-average number of shares of common stock outstanding during the period. When we are in a net loss position, in addition to excluding potentially dilutive out-of-the money securities, we exclude from our calculation of diluted net loss per share all potentially dilutive in-the-money (i) stock options, (ii) RSUs, (iii) PRSUs, (iv) unvested restricted stock in our deferred compensation plan and (v) our only outstanding warrant, and our diluted net loss per share is the same as our basic net loss per share for such periods. When we are in a net income position, the weighted-average number of shares used to calculate our diluted net income per share includes the potential dilutive effect of in-the-money securities, as determined using the treasury stock method. The following table reconciles the number of shares used to calculate basic and diluted net income (loss) per share for the periods presented, in thousands: Three months ended Six months ended 2015 2014 2015 2014 Weighted-average shares outstanding 242,067 219,682 238,903 219,453 Potentially dilutive common shares outstanding: Stock options 0 4,948 0 0 Warrant 0 609 0 0 RSUs and unvested restricted stock 0 102 0 0 Weighted-average shares used to calculate diluted net income (loss) per share 242,067 225,341 238,903 219,453 The following table presents the weighted-average number of potentially dilutive securities that were excluded from our calculation of diluted net loss per share for the periods presented, in thousands: Three months ended Six months ended 2015 2014 2015 2014 Stock options 17,671 7,455 16,815 15,446 Warrant 0 0 66 645 RSUs, PRSUs and unvested restricted stock 526 854 519 892 Total 18,197 8,309 17,400 16,983 Because the market condition for 745,000 PRSUs issued in March 2015, 695,000 PRSUs issued in March 2014, and 780,000 PRSUs issued in March 2013, was not satisfied at June 30, 2015 , such securities are excluded from the table above for the three and six months ended June 30, 2015 . Because the market condition for 780,000 PRSUs issued in March 2013, was not satisfied at June 30, 2014 , such securities are excluded from the table above for the three and six months ended June 30, 2014 .

Legal Proceedings

Legal Proceedings	6 Months Ended
	Jun. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Legal Proceedings	Legal Proceedings Beginning on September 20, 2010, a number of complaints were filed in the US District Court for the Southern District of California against us and certain of our current and former employees and directors on behalf of certain purchasers of our common stock. The complaints were brought as purported stockholder class actions, and, in general, include allegations that we and certain of our current and former employees and directors violated federal securities laws by making materially false and misleading statements regarding our BELVIQ program, thereby artificially inflating the price of our common stock. The plaintiffs sought unspecified monetary damages and other relief. On August 8, 2011, the Court consolidated the actions and appointed a lead plaintiff and lead counsel. On November 1, 2011, the lead plaintiff filed a consolidated amended complaint. On March 28, 2013, the Court dismissed the consolidated amended complaint without prejudice. On May 13, 2013, the lead plaintiff filed a second consolidated amended complaint. On November 5, 2013, the Court dismissed the second consolidated amended complaint without prejudice as to all parties except for Robert E. Hoffman, who was dismissed from the action with prejudice. On November 27, 2013, the lead plaintiff filed a motion for leave to amend the second consolidated amended complaint. On March 20, 2014, the Court denied plaintiff’s motion and dismissed the second consolidated amended complaint with prejudice. On April 18, 2014, the lead plaintiff filed a notice of appeal, and on August 27, 2014, the lead plaintiff filed his appellate brief in the US Court of Appeals for the Ninth Circuit. On October 24, 2014, we filed our answering brief in response to the lead plaintiff’s appeal. On December 5, 2014, the lead plaintiff filed his reply brief. Due to the stage of these proceedings, we are not able to predict or reasonably estimate the ultimate outcome or possible losses relating to these claims.

Issuance of Common Stock

Issuance of Common Stock	6 Months Ended
	Jun. 30, 2015
Equity [Abstract]
Issuance of Common Stock	Issuance of Common Stock In January 2015, we sold 21,000,000 shares of our common stock, par value $0.0001 per share, at a price of $4.8139 per share to the underwriters. We received approximately $100.7 million in net proceeds from this offering after deducting offering expenses.

Development, Marketing and Supp

Development, Marketing and Supply Agreement with Riovant	6 Months Ended
	Jun. 30, 2015
Roivant
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development, Marketing and Supply Agreement with Riovant	Development, Marketing and Supply Agreement with Roivant In May 2015, Arena GmbH and Roivant Sciences Ltd., or Roivant, entered into a Development, Marketing and Supply Agreement for nelotanserin, our internally discovered inverse agonist of the serotonin 2A receptor that we previously studied for insomnia before discontinuing development for such indication. Under this agreement, we granted Roivant exclusive worldwide rights to develop and commercialize nelotanserin, subject to regulatory approval. In connection with entering into the agreement, we received an upfront payment of $4.0 million from Roivant in May 2015. Revenues from this upfront payment were deferred, as we determined that the exclusive rights did not have standalone value without our ongoing development and regulatory activities. Accordingly, this payment is recognized ratably as revenue over the period in which we expect the services to be rendered. We are also eligible to receive up to $41.5 million in development and regulatory milestone payments and are eligible to receive payments from sales of nelotanserin and purchase price adjustment payments based on Roivant’s annual net product sales.

Basis of Presentation (Policies

Basis of Presentation (Policies)	6 Months Ended
	Jun. 30, 2015
Accounting Policies [Abstract]
Basis of Presentation	The accompanying unaudited condensed consolidated financial statements of Arena Pharmaceuticals, Inc., which include our wholly owned subsidiaries, 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, 2014, as filed with the Securities and Exchange Commission, or SEC, from which we derived our balance sheet as of December 31, 2014. The accompanying 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 financial statements do not include all of the information and notes required by GAAP for complete financial statements. The accompanying 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.
New Accounting Guidance	In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2014-09, “Revenue from Contracts with Customers.” ASU No. 2014-09 outlines a comprehensive revenue recognition model which will supersede most current revenue recognition guidance. ASU No. 2014-09 is effective for annual reporting periods, and interim periods within those periods, beginning after December 15, 2017. ASU No. 2014-09 allows for two methods of adoption: (a) “full retrospective” adoption, meaning the standard is applied to all periods presented, or (b) “modified retrospective” adoption, meaning the cumulative effect of applying ASU No. 2014-09 is recognized as an adjustment to the opening retained earnings balance for the year of implementation. We have not yet selected an adoption method as we are currently evaluating the impact of ASU No. 2014-09 on our consolidated financial statements. In August 2014, the FASB issued ASU No. 2014-15, “Presentation of Financial Statements – Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern.” Under GAAP, continuation of a reporting entity as a going concern is presumed as the basis for preparing financial statements unless and until the entity’s liquidation becomes imminent. Preparation of financial statements under this presumption is commonly referred to as the going concern basis of accounting. If and when an entity’s liquidation becomes imminent, financial statements should be prepared under the liquidation basis of accounting. Even when an entity’s liquidation is not imminent, there may be conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern. In those situations, financial statements should continue to be prepared under the going concern basis of accounting, but ASU No. 2014-15 should be followed to determine whether to disclose information about any relevant conditions and events. ASU No. 2014-15 is effective for the annual reporting period ending after December 15, 2016, and for annual and interim periods thereafter. We do not expect the adoption of ASU No. 2014-15 to have a material impact on our consolidated financial statements.
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.
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.
Derivative Liabilities	Our outstanding warrant was revalued on each balance sheet date, with changes in the fair value between reporting periods recorded in the interest and other income (expense) section of our condensed consolidated statements of operations and comprehensive income (loss).
Concentration of Credit Risk and Major Customers	Financial instruments, which potentially subject us to concentrations of credit risk, consist primarily of cash and cash equivalents. 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 and government-sponsored enterprise obligations and in corporate debt instruments that are rated investment grade, in accordance with an investment policy approved by our Board of Directors. Eisai and Ildong are the exclusive distributors of BELVIQ in the United States and South Korea, respectively, which are the only jurisdictions for which BELVIQ has received regulatory approval for marketing. We also produce drug products for Siegfried AG, or Siegfried, under a toll manufacturing agreement, and most of our toll manufacturing revenues are attributable to Siegfried.
Net Loss Per Share	We calculate basic and diluted net loss per share using the weighted-average number of shares of common stock outstanding during the period. When we are in a net loss position, in addition to excluding potentially dilutive out-of-the money securities, we exclude from our calculation of diluted net loss per share all potentially dilutive in-the-money (i) stock options, (ii) RSUs, (iii) PRSUs, (iv) unvested restricted stock in our deferred compensation plan and (v) our only outstanding warrant, and our diluted net loss per share is the same as our basic net loss per share for such periods. When we are in a net income position, the weighted-average number of shares used to calculate our diluted net income per share includes the potential dilutive effect of in-the-money securities, as determined using the treasury stock method.

Fair Value Disclosures (Tables)

Fair Value Disclosures (Tables)	6 Months Ended
	Jun. 30, 2015
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 at June 30, 2015 Balance Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds 1 $ 154,989 $ 154,989 $ 0 $ 0 Liabilities: Warrant derivative liabilities $ 852 $ 0 $ 852 $ 0 Fair Value Measurements at December 31, 2014 Balance Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds 1 $ 143,913 $ 143,913 $ 0 $ 0 Liabilities: Warrant derivative liabilities $ 474 $ 0 $ 474 $ 0 ______________________ (1) Included in cash and cash equivalents on our condensed consolidated balance sheets.

Inventory (Tables)

Inventory (Tables)	6 Months Ended
	Jun. 30, 2015
Inventory Disclosure [Abstract]
Components of Inventory	Inventory consisted of the following, in thousands: June 30, 2015 December 31, 2014 Raw materials $ 2,470 $ 1,167 Work in process 3,748 3,520 Finished goods at Arena GmbH 7 3,681 Finished goods at Eisai 4,112 2,463 Finished goods at Ildong 664 0 Total inventory $ 11,001 $ 10,831

Land, Property and Equipment (T

Land, Property and Equipment (Tables)	6 Months Ended
	Jun. 30, 2015
Property, Plant and Equipment [Abstract]
Land, Property and Equipment	Land, property and equipment consisted of the following, in thousands: June 30, 2015 December 31, 2014 Cost $ 179,157 $ 174,938 Less accumulated depreciation and amortization (97,745 ) (92,019 ) Land, property and equipment, net $ 81,412 $ 82,919

Accounts Payable and Other Ac23

Accounts Payable and Other Accrued Liabilities (Tables)	6 Months Ended
	Jun. 30, 2015
Payables and Accruals [Abstract]
Accounts Payable and Other Accrued Liabilities	Accounts payable and other accrued liabilities consisted of the following, in thousands: June 30, 2015 December 31, 2014 Accounts payable $ 2,662 $ 2,844 Accrued compensation 4,409 4,792 Other accrued liabilities 1,144 2,573 Total accounts payable and other accrued liabilities $ 8,215 $ 10,209

Marketing and Supply Agreemen24

Marketing and Supply Agreement with Eisai (Tables)	6 Months Ended
	Jun. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenues Recognized under Eisai Agreement	The following table summarizes the revenues we recognized under our collaboration with Eisai for the periods presented, in thousands: Three months ended Six months ended 2015 2014 2015 2014 Net product sales $ 3,893 $ 3,529 $ 8,329 $ 6,411 Amortization of upfront payments 1,885 1,885 3,770 3,860 Reimbursement of development expenses 1,156 6,568 1,347 7,313 Milestone payment 0 0 0 500 Reimbursement of patent and trademark expenses 172 101 232 228 Subtotal other Eisai collaborative revenue 3,213 8,554 5,349 11,901 Total $ 7,106 $ 12,083 $ 13,678 $ 18,312
Deferred Revenues Attributable to Eisa	The following table summarizes the deferred revenues under our collaboration with Eisai, in thousands: June 30, 2015 December 31, 2014 Upfront payments $ 90,704 $ 94,474 Net product sales 16,833 7,081 Total deferred revenues attributable to Eisai 107,537 101,555 Less current portion (24,374 ) (14,622 ) Deferred revenues attributable to Eisai, less current portion $ 83,163 $ 86,933
Summary of Cost Sharing Allocation	The chart below summarizes the general agreement regarding cost sharing between Eisai and us for significant development activities under the Eisai Agreement. In addition, Eisai or we may from time to time conduct approved development of lorcaserin at such party’s own expense. Eisai Second Amended and Restated Marketing and Supply Agreement: Cost Sharing for Development United States Rest of North and South America Remaining Territories BELVIQ - Pre-approval* Not Applicable General Eisai: 90%; Arena: 10% Certain stability work Eisai: 50%; Arena: 50% Up to a total of $100.0 million - Eisai: 50%; Arena: 50% Thereafter, Eisai: 100% BELVIQ - Post-approval* General Eisai: 90%; Arena 10% Non-FDA required portion of CVOT Up to $80.0 million - Eisai: 50%; Arena: 50% Thereafter, Eisai: 100% Certain pediatric studies Eisai: 50%; Arena: 50% General Eisai: 90%; Arena: 10% Certain stability work Eisai: 50%; Arena: 50% Up to a total of $50.0 million - Eisai: 50%; Arena: 50% Thereafter, Eisai: 90%; Arena: 10% Lorcaserin products other than BELVIQ - Pre-approval Up to a total of $250.0 million (as reduced by up to $80.0 million for non-FDA required portion of CVOT) -Eisai: 50%; Arena: 50% Lorcaserin products other than BELVIQ - Post-approval Up to a total of $100.0 million in the aggregate across all additional products - Eisai: 50%; Arena: 50% Thereafter, Eisai: 90%; Arena: 10% ______________________ * Development required by a regulatory authority, with the exception of the non-FDA required portions of the CVOT.

Share-based Activity (Tables)

Share-based Activity (Tables)	6 Months Ended
	Jun. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share Based Compensation Expense	We recognized share-based compensation expense as follows, in thousands: Three months ended Six months ended 2015 2014 2015 2014 Research and development $ 2,185 $ 1,742 $ 4,241 $ 3,523 General and administrative 1,929 1,600 3,706 3,020 Total share-based compensation expense $ 4,114 $ 3,342 $ 7,947 $ 6,543 Total share-based compensation expense capitalized into inventory $ 43 $ 39 $ 105 $ 39
Summary of Stock Option Activity	The following table summarizes our stock option activity during the six months ended June 30, 2015 , in thousands (except per share data): Options Weighted- Average Exercise Price Outstanding at January 1, 2015 15,831 $ 5.25 Granted 3,037 4.47 Exercised (745 ) 2.06 Forfeited/cancelled/expired (565 ) 6.33 Outstanding at June 30, 2015 17,558 $ 5.21
Summary of Restricted Stock Unit Awards Activity	The following table summarizes activity with respect to our time-based restricted stock unit awards, or RSUs, during the six months ended June 30, 2015 , in thousands (except per share data): RSUs Weighted- Average Grant-Date Fair Value Unvested at January 1, 2015 456 $ 5.72 Granted 281 4.11 Vested (88 ) 6.50 Forfeited/cancelled 0 Unvested at June 30, 2015 649 $ 4.92
Assumptions used to Value Performance Restricted Stock Unit Awards Granted and Estimated Grant Date Fair Value	The following table sets forth the assumptions used to value the PRSUs granted in March 2015 and their estimated grant-date fair value: Risk-free interest rate 1.1 % Dividend yield 0 % Expected volatility 75 % Remaining performance period (years) 2.97 Estimated fair value per share of PRSUs granted $ 4.50

Concentrations of Credit Risk26

Concentrations of Credit Risk and Major Customers (Tables)	6 Months Ended
	Jun. 30, 2015
Risks and Uncertainties [Abstract]
Percentages of Total Revenues	Percentages of our total revenues are as follows: Three months ended Six months ended 2015 2014 2015 2014 Eisai Agreement 77.4 % 94.4 % 63.8 % 93.4 % Ildong Agreement 5.3 % 0.7 % 26.9 % 0.9 % Toll manufacturing agreements 15.2 % 4.5 % 8.1 % 5.2 % Other collaborative agreements 2.1 % 0.4 % 1.2 % 0.5 % Total percentage of revenues 100.0 % 100.0 % 100.0 % 100.0 %

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	6 Months Ended
	Jun. 30, 2015
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table reconciles the number of shares used to calculate basic and diluted net income (loss) per share for the periods presented, in thousands: Three months ended Six months ended 2015 2014 2015 2014 Weighted-average shares outstanding 242,067 219,682 238,903 219,453 Potentially dilutive common shares outstanding: Stock options 0 4,948 0 0 Warrant 0 609 0 0 RSUs and unvested restricted stock 0 102 0 0 Weighted-average shares used to calculate diluted net income (loss) per share 242,067 225,341 238,903 219,453
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 loss per share for the periods presented, in thousands: Three months ended Six months ended 2015 2014 2015 2014 Stock options 17,671 7,455 16,815 15,446 Warrant 0 0 66 645 RSUs, PRSUs and unvested restricted stock 526 854 519 892 Total 18,197 8,309 17,400 16,983

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	Jun. 30, 2015	Dec. 31, 2014
Assets:
Money market funds	$ 154,989	$ 143,913
Liabilities:
Warrant derivative liabilities	852	474
Quoted Prices in Active Markets (Level 1)
Assets:
Money market funds	154,989	143,913
Liabilities:
Warrant derivative liabilities	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Money market funds	0	0
Liabilities:
Warrant derivative liabilities	852	474
Significant Unobservable Inputs (Level 3)
Assets:
Money market funds	0	0
Liabilities:
Warrant derivative liabilities	$ 0	$ 0

Inventory - Components of Inven

Inventory - Components of Inventory (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Inventory [Line Items]
Raw materials	$ 2,470	$ 1,167
Work in process	3,748	3,520
Inventory	11,001	10,831	[1]
Arena GmbH
Inventory [Line Items]
Finished goods	7	3,681
Eisai
Inventory [Line Items]
Finished goods	4,112	2,463
Ildong
Inventory [Line Items]
Finished goods	$ 664	$ 0
[1]	The balance sheet data at December 31, 2014, has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by US generally accepted accounting principles for complete financial statements.

Land, Property and Equipment (D

Land, Property and Equipment (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Cost	$ 179,157	$ 174,938
Less accumulated depreciation and amortization	(97,745)	(92,019)
Land, property and equipment, net	$ 81,412	$ 82,919	[1]
[1]	The balance sheet data at December 31, 2014, has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by US generally accepted accounting principles for complete financial statements.

Accounts Payable and Other Ac31

Accounts Payable and Other Accrued Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Accounts payable	$ 2,662	$ 2,844
Accrued compensation	4,409	4,792
Other accrued liabilities	1,144	2,573
Total accounts payable and other accrued liabilities	$ 8,215	$ 10,209	[1]
[1]	The balance sheet data at December 31, 2014, has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by US generally accepted accounting principles for complete financial statements.

Derivative Liabilities - Additi

Derivative Liabilities - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jun. 30, 2015	Dec. 31, 2014	[1]	Aug. 31, 2008
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Issuance of warrant to purchase stock, number of shares				1,106,344
Original exercise price of warrant ($ per warrant)				$ 7.71
Adjustment price of warrant in anti-dilution provision ($ per warrant)	$ 6.72
Revised exercise price of warrant ($ per warrant)	$ 4.34
Warrant outstanding (number of warrants)	1,965,418
Derivative liabilities, current	$ 852	$ 474
[1]	The balance sheet data at December 31, 2014, has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by US generally accepted accounting principles for complete financial statements.

Marketing and Supply Agreemen33

Marketing and Supply Agreement with Eisai - Additional Information (Detail)	1 Months Ended				3 Months Ended		6 Months Ended		60 Months Ended
	Jan. 31, 2015$ / prescription	Nov. 30, 2013USD ($)	May. 31, 2012USD ($)	Jul. 31, 2010USD ($)	Jun. 30, 2015USD ($)	Jun. 30, 2014USD ($)	Jun. 30, 2015USD ($)	Jun. 30, 2014USD ($)	Jun. 30, 2015USD ($)	Dec. 31, 2014USD ($)	[1]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales					$ 4,285,000	$ 3,529,000	$ 10,903,000	$ 6,411,000
Payable to Eisai					10,031,000		10,031,000		$ 10,031,000	$ 23,705,000
Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Recognized milestone revenue					0	0	0	500,000
Net product sales					3,893,000	$ 3,529,000	8,329,000	$ 6,411,000
Payable to Eisai					10,031,000		10,031,000		10,031,000
Maximum | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Prescription cost for patients without commercial coverage | $ / prescription	75
Minimum | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Copay threshold for patients with commercial coverage | $ / prescription	50
Product Purchase Price | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales					3,800,000		7,800,000
Voucher Redemption | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales					100,000		500,000
UNITED STATES | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Purchase price range minimum		31.50%
Purchase price range maximum		36.50%
Annual net product sales threshold for maximum purchase price		$ 750,000,000
Non US Territories Other Than Europe, China and Japan | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Purchase price range minimum		30.75%
Purchase price range maximum		35.75%
Annual net product sales threshold for maximum purchase price		$ 750,000,000
Europe, China and Japan | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Purchase price range minimum		27.50%
Purchase price range maximum		35.00%
Annual net product sales threshold for maximum purchase price		$ 500,000,000
Original Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative agreement initiation date				2010-07
Collaborative agreement upfront payments				$ 50,000,000
Collaborative agreement, revenue recognition period				16 years
Eisai First Amended Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative agreement initiation date			2012-05
Collaborative agreement upfront payments			$ 5,000,000
Collaborative agreement, revenue recognition period			15 years
Eisai Second Amended Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative agreement initiation date		2013-11
Collaborative agreement upfront payments		$ 60,000,000
Collaborative agreement, revenue recognition period		15 years
Recognized milestone revenue									86,500,000
Additional milestone payments on achievement					176,000,000		176,000,000		176,000,000
Aggregate one-time purchase price adjustments					1,560,000,000		1,560,000,000		1,560,000,000
Eisai Second Amended Agreement | All Territories
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate one-time purchase price adjustments					1,190,000,000		1,190,000,000		1,190,000,000
First annual net sales threshold to earn purchase price adjustments in all territories		$ 250,000,000
Last annual net sales threshold to earn purchase price adjustments in all territories		2,500,000,000
Portion of purchase price adjustment payments		330,000,000
Annual net sales threshold to earn portion of purchase price adjustments in all territories		1,000,000,000
Eisai Second Amended Agreement | All Non-US territories
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional one-time purchase price adjustment payments					370,000,000		370,000,000		370,000,000
Eisai Second Amended Agreement | Non-US Territories in North and South America
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional one-time purchase price adjustment payments					185,000,000		185,000,000		185,000,000
First annual net sales threshold to earn purchase price adjustments outside of the US		100,000,000
Last annual net sales threshold to earn additional purchase price adjustments outside of the US		1,000,000,000
Eisai Second Amended Agreement | Territories Outside of North and South America
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Additional one-time purchase price adjustment payments					$ 185,000,000		$ 185,000,000		$ 185,000,000
First annual net sales threshold to earn purchase price adjustments outside of the US		100,000,000
Last annual net sales threshold to earn additional purchase price adjustments outside of the US		$ 1,000,000,000
[1]	The balance sheet data at December 31, 2014, has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by US generally accepted accounting principles for complete financial statements.

Marketing and Supply Agreemen34

Marketing and Supply Agreement with Eisai - Revenues Recognized under Collaboration with Eisai (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales	$ 4,285	$ 3,529	$ 10,903	$ 6,411
Total revenues	9,181	12,801	21,437	19,615
Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales	3,893	3,529	8,329	6,411
Amortization of upfront payments	1,885	1,885	3,770	3,860
Milestone payment	0	0	0	500
Subtotal other Eisai collaborative revenue	3,213	8,554	5,349	11,901
Total revenues	7,106	12,083	13,678	18,312
Eisai | Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement of expenses	1,156	6,568	1,347	7,313
Eisai | Patent and trademark expenses
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement of expenses	$ 172	$ 101	$ 232	$ 228

Marketing and Supply Agreemen35

Marketing and Supply Agreement with Eisai - Deferred Revenues under Collaboration with Eisai (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Deferred Revenue Arrangement [Line Items]
Less current portion	$ (26,917)	$ (15,238)	[1]
Deferred revenues, less current portion	92,648	93,064	[1]
Eisai
Deferred Revenue Arrangement [Line Items]
Total deferred revenues	107,537	101,555
Less current portion	(24,374)	(14,622)
Deferred revenues, less current portion	83,163	86,933
Eisai | Upfront payments
Deferred Revenue Arrangement [Line Items]
Total deferred revenues	90,704	94,474
Eisai | Net product sales
Deferred Revenue Arrangement [Line Items]
Total deferred revenues	$ 16,833	$ 7,081
[1]	The balance sheet data at December 31, 2014, has been derived from audited financial statements at that date. It does not include, however, all of the information and notes required by US generally accepted accounting principles for complete financial statements.

Marketing and Supply Agreemen36

Marketing and Supply Agreement with Eisai - Summary of Cost Sharing Allocation (Detail) - 6 months ended Jun. 30, 2015 - USD ($)	Total
Belviq Product Pre Approval Up To One Hundred Million Dollars | Territories Outside of North and South America | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate expense cap on equal split of development expenses	$ 100,000,000
Portion of expenses	50.00%
Belviq Product Pre Approval Up To One Hundred Million Dollars | Territories Outside of North and South America | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%
Belviq Product Pre Approval More Than One Hundred Million Dollars | Territories Outside of North and South America | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	100.00%
Belviq Product Post Approval Up To Fifty Million Dollars | Territories Outside of North and South America | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate expense cap on equal split of development expenses	$ 50,000,000
Portion of expenses	50.00%
Belviq Product Post Approval Up To Fifty Million Dollars | Territories Outside of North and South America | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%
Belviq Product Post Approval More Than Fifty Million Dollars | Territories Outside of North and South America | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	10.00%
Belviq Product Post Approval More Than Fifty Million Dollars | Territories Outside of North and South America | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	90.00%
Belviq Product Pre Approval | Non-US Territories in North and South America | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	10.00%
Belviq Product Pre Approval | Non-US Territories in North and South America | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	90.00%
Belviq Product Pre Approval Certain Stability Work | Non-US Territories in North and South America | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%
Belviq Product Pre Approval Certain Stability Work | Non-US Territories in North and South America | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%
Belviq Product Post Approval | Non-US Territories in North and South America | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	10.00%
Belviq Product Post Approval | Non-US Territories in North and South America | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	90.00%
Belviq Product Post Approval | UNITED STATES | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	10.00%
Belviq Product Post Approval | UNITED STATES | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	90.00%
Belviq Product Post Approval Certain Stability Work | Non-US Territories in North and South America | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%
Belviq Product Post Approval Certain Stability Work | Non-US Territories in North and South America | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%
Belviq Product Post Approval Certain Pediatric Studies | UNITED STATES | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%
Belviq Product Post Approval Certain Pediatric Studies | UNITED STATES | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%
Belviq Product Post Approval Non Fda Required Portion Of Cardiovascular Outcomes Trial Up To Eighty Million Dollars | UNITED STATES | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate expense cap on equal split of development expenses	$ 80,000,000
Portion of expenses	50.00%
Belviq Product Post Approval Non Fda Required Portion Of Cardiovascular Outcomes Trial Up To Eighty Million Dollars | UNITED STATES | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%
Belviq Product Post Approval Non Fda Required Portion Of Cardiovascular Outcomes Trial More Than Eighty Million Dollars | UNITED STATES | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	100.00%
Lorcaserin Product Other Than Belviq Pre Approval | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%
Lorcaserin Product Other Than Belviq Pre Approval | Arena GmbH | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate expense cap on equal split of development expenses	$ 250,000,000
Lorcaserin Product Other Than Belviq Pre Approval | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%
Lorcaserin Product Other Than Belviq Post Approval Up To One Hundred Million Dollars | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate expense cap on equal split of development expenses	$ 100,000,000
Portion of expenses	50.00%
Lorcaserin Product Other Than Belviq Post Approval Up To One Hundred Million Dollars | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%
Lorcaserin Product Other Than Belviq Post Approval More Than One Hundred Million Dollars | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	10.00%
Lorcaserin Product Other Than Belviq Post Approval More Than One Hundred Million Dollars | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	90.00%

Marketing and Supply Agreemen37

Marketing and Supply Agreement with Ildong (Detail) - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended
	Mar. 31, 2015	Nov. 30, 2012	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales			$ 4,285,000	$ 3,529,000	$ 10,903,000	$ 6,411,000
Ildong
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative agreement upfront payments		$ 5,000,000
Collaborative agreement, revenue recognition period		14 years
Milestone payment	$ 3,000,000
Purchase price range minimum		35.00%
Purchase price range maximum		45.00%
Annual net product sales threshold for maximum purchase price		$ 15,000,000
Net product sales			$ 400,000		$ 2,600,000

Share-based Activity - Share Ba

Share-based Activity - Share Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 4,114	$ 3,342	$ 7,947	$ 6,543
Total share-based compensation expense capitalized into inventory	43	39	105	39
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	2,185	1,742	4,241	3,523
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 1,929	$ 1,600	$ 3,706	$ 3,020

Share-based Activity - Summary

Share-based Activity - Summary of Stock Option Activity (Detail) - 6 months ended Jun. 30, 2015 - Stock options - $ / shares shares in Thousands	Total
Number of stock options
Outstanding at January 1, 2015	15,831
Granted	3,037
Exercised	(745)
Forfeited/cancelled/expired	(565)
Outstanding at June 30, 2015	17,558
Weighted- Average Exercise Price
Outstanding at January 1, 2015	$ 5.25
Granted	4.47
Exercised	2.06
Forfeited/cancelled/expired	6.33
Outstanding at June 30, 2015	$ 5.21

Share-based Activity - Summar40

Share-based Activity - Summary of Restricted Stock Unit Awards Activity (Detail) - 6 months ended Jun. 30, 2015 - Restricted Stock Units (RSU) - $ / shares shares in Thousands	Total
Number of Restricted Stock Units
Unvested at January 1, 2015	456
Granted	281
Vested	(88)
Forfeited/cancelled	0
Unvested at June 30, 2015	649
Weighted- Average Grant-Date Fair Value
Unvested at January 1, 2015	$ 5.72
Granted	4.11
Vested	6.50
Unvested at June 30, 2015	$ 4.92

Share-based Activity - Addition

Share-based Activity - Additional Information (Detail) $ in Millions	1 Months Ended
	Mar. 31, 2015USD ($)shares	Mar. 31, 2014shares	Mar. 31, 2013shares	Jun. 30, 2015USD ($)
Stockholders Equity [Line Items]
Multiplier of grant-date fair value for cap on number of PRSUs that may be granted	6
Performance restricted stock units
Stockholders Equity [Line Items]
Units granted (shares)	745,000	695,000	780,000
Cap on percentage of funding if the absolute 3-year TSR is negative	100.00%
Vesting period	3 years
PRSU grant-date fair value | $	$ 3.4
Aggregate intrinsic value of units outstanding | $				$ 10.3
Performance restricted stock units | Share Based Compensation
Stockholders Equity [Line Items]
Units granted (shares)	745,000
Performance restricted stock units | Minimum
Stockholders Equity [Line Items]
Number of shares to be awarded as a percentage of target amounts	0.00%
Performance restricted stock units | Maximum
Stockholders Equity [Line Items]
Number of shares to be awarded as a percentage of target amounts	200.00%

Share-based Activity - Assumpti

Share-based Activity - Assumptions and Estimated Fair Value of Performance Restricted Stock Unit Awards (Detail) - 6 months ended Jun. 30, 2015 - Performance restricted stock units - $ / shares	Total
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.10%
Dividend yield	0.00%
Expected volatility	75.00%
Remaining performance period (years)	2 years 11 months 19 days
Estimated fair value per share of PRSUs granted	$ 4.50

Concentrations of Credit Risk43

Concentrations of Credit Risk and Major Customers - Percentages of Total Revenues (Detail) - Sales Revenue, Net	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Concentration Risk [Line Items]
Percentage of revenues	100.00%	100.00%	100.00%	100.00%
Eisai Agreement
Concentration Risk [Line Items]
Percentage of revenues	77.40%	94.40%	63.80%	93.40%
Ildong Agreement
Concentration Risk [Line Items]
Percentage of revenues	5.30%	0.70%	26.90%	0.90%
Toll manufacturing agreements
Concentration Risk [Line Items]
Percentage of revenues	15.20%	4.50%	8.10%	5.20%
Other collaborative agreements
Concentration Risk [Line Items]
Percentage of revenues	2.10%	0.40%	1.20%	0.50%

Net Income (Loss) Per Share - S

Net Income (Loss) Per Share - Shares Outstanding (Detail) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Incremental Dilutive Effect (in shares)
Basic	242,067	219,682	238,903	219,453
Weighted-average shares used to calculate diluted net income (loss) per share	242,067	225,341	238,903	219,453
Stock options
Incremental Dilutive Effect (in shares)
Stock options	0	4,948	0	0
Warrant
Incremental Dilutive Effect (in shares)
Warrant	0	609	0	0
RSUs, PRSUs and unvested restricted stock
Incremental Dilutive Effect (in shares)
Stock options	0	102	0	0

Net Income (Loss) Per Share - P

Net Income (Loss) Per Share - Potentially Dilutive Securities Excluded From Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities excluded from calculation of diluted net loss per share (shares)	18,197	8,309	17,400	16,983
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)	17,671	7,455	16,815	15,446
Warrant
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities excluded from calculation of diluted net loss per share (shares)	0	0	66	645
RSUs, PRSUs 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)	526	854	519	892

Net Income (Loss) Per Share - A

Net Income (Loss) Per Share - Additional Information (Detail) - shares	1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Performance restricted stock units
Earnings Per Share [Line Items]
Units granted (shares)	745,000	695,000	780,000

Issuance of Common Stock - Addi

Issuance of Common Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	6 Months Ended
	Jan. 31, 2015	Jun. 30, 2015	Jun. 30, 2014
Equity [Abstract]
Issuance of common stock	21,000,000
Common stock, par value ($ per share)	$ 0.0001
Sale of stock, price per share ($ per share)	$ 4.8139
Net proceeds from sale of common stock	$ 100,700	$ 102,663	$ 4,258

Development, Marketing and Su48

Development, Marketing and Supply Agreement with Riovant - Additional Information (Detail) - Roivant - USD ($)	1 Months Ended
	May. 31, 2015	Jun. 30, 2015
Subsequent Event [Line Items]
Expected collaborative agreement upfront payment	$ 4,000,000
Additional milestone payments on achievement		$ 41,500,000