Arena Pharmaceuticals (ARNA) 10-Q 11 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	6-May-15
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Trading Symbol	ARNA
Entity Registrant Name	ARENA PHARMACEUTICALS INC
Entity Central Index Key	1080709
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		242,039,838

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$240,981	$163,209	[1]
Accounts receivable	12,209	3,712	[1]
Inventory	11,386	10,831	[1]
Prepaid expenses and other current assets	4,048	4,144	[1]
Total current assets	268,624	181,896	[1]
Land, property and equipment, net	82,096	82,919	[1]
Intangibles, net	8,500	8,482	[1]
Other non-current assets	3,069	3,088	[1]
Total assets	362,289	276,385	[1]
Current liabilities:
Accounts payable and other accrued liabilities	7,124	10,209	[1]
Accrued clinical and preclinical study fees	5,449	7,027	[1]
Payable to Siegfried for acquisition of land and building	8,396	8,217	[1]
Current portion of deferred revenues	26,291	15,238	[1]
Derivative liabilities	2,023	474	[1]
Current portion of lease financing obligations	2,609	2,492	[1]
Total current liabilities	74,364	67,362	[1]
Deferred rent	398	369	[1]
Deferred revenues, less current portion	91,035	93,064	[1]
Lease financing obligations, less current portion	67,558	68,245	[1]
Commitments and contingencies			[1]
Stockholders' equity:
Common stock	24	22	[1]
Additional paid-in capital	1,418,683	1,312,656	[1]
Accumulated other comprehensive income	2,763	2,908	[1]
Accumulated deficit	-1,292,536	-1,268,241	[1]
Total stockholders' equity	128,934	47,345	[1]
Total liabilities and stockholders' equity	362,289	276,385	[1]
Eisai
Current liabilities:
Payable to Eisai	22,472	23,705	[1]
Current portion of deferred revenues	25,347	14,622
Deferred revenues, less current portion	$85,048	$86,933
[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_Stateme

Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) (USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Revenues:
Net product sales	$6,618	$2,882
Toll manufacturing	346	448
Total revenues	12,256	6,814
Operating Costs and Expenses:
Cost of product sales	3,191	831
Cost of toll manufacturing	402	496
Research and development	21,968	20,988
General and administrative	8,439	8,037
Total operating costs and expenses	34,000	30,352
Loss from operations	-21,744	-23,538
Interest and Other Income (Expense):
Interest income	34	29
Interest expense	-1,696	-1,747
Loss from valuation of derivative liabilities	-1,549	-110
Other	660	111
Total interest and other expense, net	-2,551	-1,717
Net loss	-24,295	-25,255
Net loss per share:
Basic	($0.10)	($0.12)
Diluted	($0.10)	($0.12)
Shares used in calculating net loss per share:
Basic	235,703	219,222
Diluted	235,703	219,222
Comprehensive Income (Loss):
Net loss	-24,295	-25,255
Foreign currency translation gain (loss)	-145	91
Unrealized gain on available-for-sale securities	0	53,234
Comprehensive income (loss)	-24,440	28,070
Eisai
Revenues:
Net product sales	4,436	2,882
Other collaborative revenue	2,136	3,347
Total revenues	6,572	6,229
Other
Revenues:
Other collaborative revenue	$3,156	$137

Condensed_Consolidated_Stateme1

Condensed Consolidated Statements of Cash Flows (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Operating Activities
Net loss	($24,295)		($25,255)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,425		1,992
Amortization of intangibles	27		181
Share-based compensation	3,833		3,201
Loss from valuation of derivative liabilities	1,549		110
Amortization of prepaid financing costs	34		34
Gain on sale of equipment	0		-45
Changes in assets and liabilities:
Accounts receivable	-8,612		8,934
Inventory	-197		903
Prepaid expenses and other assets	257		-2,806
Payables and accrued liabilities	-6,711		-1,613
Deferred revenues	8,644		-4,786
Deferred rent	29		34
Net cash used in operating activities	-23,017		-19,116
Investing Activities
Purchases of property and equipment	-1,069		-2,469
Proceeds from sale of equipment	0		45
Other non-current assets	0		209
Net cash used in investing activities	-1,069		-2,215
Financing Activities
Principal payments on lease financing obligations	-570		-466
Proceeds from issuance of common stock	101,979		2,927
Net cash provided by financing activities	101,409		2,461
Effect of exchange rate changes on cash	449		264
Net increase (decrease) in cash and cash equivalents	77,772		-18,606
Cash and cash equivalents at beginning of period	163,209	[1]	221,878
Cash and cash equivalents at end of period	$240,981		$203,272
[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	3 Months Ended
	Mar. 31, 2015
Basis of Presentation	1. 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. As issued, ASU No. 2014-09 is effective for annual reporting periods, and interim periods within those periods, beginning after December 15, 2016; however, in April 2015, the FASB issued a proposal to defer the effective date of ASU No. 2014-09 such that it would be 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 the 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.
	In April 2015, the FASB issued ASU No. 2015-05, “Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement.” ASU No. 2015-05 provides guidance to customers about whether a cloud computing arrangement includes a software license. If a cloud computing arrangement includes a software license, the customer should account for the software license element of the arrangement consistent with the acquisition of other software licenses. If a cloud computing arrangement does not include a software license, the customer should account for the arrangement as a service contract. The new guidance does not change the accounting for a customer’s accounting for service contracts. ASU No. 2015-05 is effective for interim and annual reporting periods beginning after December 15, 2015. We do not expect the adoption of ASU No. 2015-05 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	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures	2. 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 March 31, 2015
			Balance			Quoted Prices in		Significant Other		Significant
						Active Markets		Observable		Unobservable Inputs
						(Level 1)		Inputs		(Level 3)
								(Level 2)
	Assets:
	Money market funds1		$	208,947		$	208,947	$	0	$	0
	Liabilities:
	Warrant derivative liabilities		$	2,023		$	0	$	2,023	$	0
			Fair Value Measurements at December 31, 2014
			Balance			Quoted Prices in		Significant Other		Significant
						Active Markets		Observable		Unobservable Inputs
						(Level 1)		Inputs		(Level 3)
								(Level 2)
	Assets:
	Money market funds1		$	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	3 Months Ended
	Mar. 31, 2015
Inventory	3. Inventory
	Inventory consisted of the following, in thousands:
		March 31,		December 31,
		2015		2014
	Raw materials	$	2,247	$	1,167
	Work in process		3,937		3,520
	Finished goods at Arena GmbH		4		3,681
	Finished goods at Eisai		4,943		2,463
	Finished goods at Ildong		255		0
	Total inventory	$	11,386	$	10,831

Land_Property_and_Equipment

Land, Property and Equipment	3 Months Ended
	Mar. 31, 2015
Land, Property and Equipment	4. Land, Property and Equipment
	Land, property and equipment consisted of the following, in thousands:
		March 31,			December 31,
		2015			2014
	Cost	$	176,619		$	174,938
	Less accumulated depreciation and amortization		(94,523	)		(92,019	)
	Land, property and equipment, net	$	82,096		$	82,919

Accounts_Payable_and_Other_Acc

Accounts Payable and Other Accrued Liabilities	3 Months Ended
	Mar. 31, 2015
Accounts Payable and Other Accrued Liabilities	5. Accounts Payable and Other Accrued Liabilities
	Accounts payable and other accrued liabilities consisted of the following, in thousands:
		March 31,		December 31,
		2015		2014
	Accounts payable	$	1,957	$	2,844
	Accrued compensation		3,839		4,792
	Other accrued liabilities		1,328		2,573
	Total accounts payable and other accrued liabilities	$	7,124	$	10,209

Derivative_Liabilities

Derivative Liabilities	3 Months Ended
	Mar. 31, 2015
Derivative Liabilities	6. 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 March 31, 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 $2.0 million and $0.5 million at March 31, 2015, and December 31, 2014, respectively, is recorded as a current derivative liability on our condensed consolidated balance sheets.
	Our outstanding warrant is 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	3 Months Ended
	Mar. 31, 2015
Eisai
Marketing and Supply Agreement	7. 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
			March 31,
			2015			2014
	Net product sales		$	4,436		$	2,882
	Amortization of upfront payments			1,885			1,975
	Reimbursement of development expenses			191			745
	Milestone payment			0			500
	Reimbursement of patent and trademark expenses			60			127
	Subtotal other Eisai collaborative revenue			2,136			3,347
	Total		$	6,572		$	6,229
	The following table summarizes the deferred revenues under our collaboration with Eisai, in thousands:
			March 31,			December 31,
			2015			2014
	Upfront payments		$	92,589		$	94,474
	Net product sales			17,806			7,081
	Total deferred revenues attributable to Eisai			110,395			101,555
	Less current portion			(25,347	)		(14,622	)
	Deferred revenues attributable to Eisai, less current portion		$	85,048		$	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, and 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 March 31, 2015, we recognized revenues from net product sales of BELVIQ to Eisai of $4.4 million, of which $4.0 million related to sales at the Eisai Product Purchase Price and $0.4 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 $22.5 million classified as Payable to Eisai on our condensed consolidated balance sheet at March 31, 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. We expect to pay approximately $10 million to $11 million to Eisai in May 2015 for the annual refund for product sold by Eisai to their distributors.
	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	Remaining Territories
					North and South America
	BELVIQ		Not Applicable		General	Up to a total of $100.0 million -
	- Pre-approval*				Eisai: 90%; Arena: 10%	Eisai: 50%; Arena: 50%
					Certain stability work Eisai: 50%; Arena: 50%	Thereafter, Eisai: 100%
	BELVIQ		General		General	Up to a total of $50.0 million -
	- Post-approval*		Eisai: 90%; Arena 10%		Eisai: 90%; Arena: 10%	Eisai: 50%; Arena: 50%
			Non-FDA required portion of CVOT		Certain stability work	Thereafter, Eisai: 90%;
			Up to $80.0 million -		Eisai: 50%; Arena: 50%	Arena: 10%
			Eisai: 50%; Arena: 50%
			Thereafter, Eisai: 100%
			Certain pediatric studies
			Eisai: 50%; Arena: 50%
	Lorcaserin		Up to a total of $250.0 million (as reduced by up to $80.0 million for non-FDA required portion of CVOT)
	products other than		-Eisai: 50%; Arena: 50%
	BELVIQ
	- Pre-approval
	Lorcaserin		Up to a total of $100.0 million in the aggregate across all additional products -
	products other than		Eisai: 50%; Arena: 50%
	BELVIQ		Thereafter, Eisai: 90%; Arena: 10%
	- Post-approval
	*	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.
lldong
Marketing and Supply Agreement	8. 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 months ended March 31, 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 net product sales of BELVIQ to Ildong of $2.2 million for the three months ended March 31, 2015.

Sharebased_Activity

Share-based Activity	3 Months Ended
	Mar. 31, 2015
Share-based Activity	9. Share-based Activity
	Share-based Compensation.
	We recognized share-based compensation expense as follows, in thousands:
		Three months ended
		March 31,
		2015			2014
	Research and development	$	2,056		$	1,781
	General and administrative		1,777			1,420
	Total share-based compensation expense	$	3,833		$	3,201
	Total share-based compensation expense capitalized into inventory	$	62		$	0
	Share-based Award Activity.
	The following table summarizes our stock option activity during the three months ended March 31, 2015, in thousands (except per share data):
		Options			Weighted-
					Average
					Exercise Price
	Outstanding at January 1, 2015		15,831		$	5.25
	Granted		2,999			4.48
	Exercised		(603	)		2.05
	Forfeited/cancelled/expired		(493	)		6.3
	Outstanding at March 31, 2015		17,734		$	5.2
	The following table summarizes activity with respect to our time-based restricted stock unit awards, or RSUs, during the three months ended March 31, 2015, in thousands (except per share data):
		RSUs			Weighted-
					Average
					Grant-Date
					Fair Value
	Unvested at January 1, 2015		456		$	5.72
	Granted		0
	Vested		(44	)		6.5
	Forfeited/cancelled		0
	Unvested at March 31, 2015		412		$	5.64
	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	$	4.5
	The aggregate intrinsic value of all of the outstanding PRSUs granted to date at March 31, 2015, was $9.7 million. All of the PRSUs granted to date were outstanding and unvested at March 31, 2015.

Concentrations_of_Credit_Risk_

Concentrations of Credit Risk and Major Customers	3 Months Ended
	Mar. 31, 2015
Concentrations of Credit Risk and Major Customers	10. 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 all of our toll manufacturing revenues are attributable to Siegfried.
	Percentages of our total revenues are as follows:
		Three months ended
		March 31,
		2015			2014
	Eisai Agreement		53.6	%		91.4	%
	Ildong Agreement		43	%		1.3	%
	Toll manufacturing agreement with Siegfried		2.8	%		6.6	%
	Other collaborative agreements		0.6	%		0.7	%
	Total percentage of revenues		100	%		100	%

Net_Loss_Per_Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2015
Net Loss Per Share	11. 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.
	Since we are in a net loss position, in addition to excluding potentially dilutive out-of-the money securities, we have excluded 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. 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
		March 31,
		2015		2014
	Stock options		15,949		14,962
	Warrant		131		679
	RSUs, PRSUs and unvested restricted stock		512		766
	Total		16,592		16,407
	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 March 31, 2015, such securities are excluded from the table above for the three months ended March 31, 2015. Because the market condition for 780,000 PRSUs issued in March 2013, was not satisfied at March 31, 2014, such securities are excluded from the table above for the three months ended March 31, 2014.

Legal_Proceedings

Legal Proceedings	3 Months Ended
	Mar. 31, 2015
Legal Proceedings	12. 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	3 Months Ended
	Mar. 31, 2015
Issuance of Common Stock	13. 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.

Subsequent_Event

Subsequent Event	3 Months Ended
	Mar. 31, 2015
Subsequent Event	14. Subsequent Event
	On May 8, 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 expect to receive an upfront payment of $4.0 million from Roivant in May 2015. 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)	3 Months Ended
	Mar. 31, 2015
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. As issued, ASU No. 2014-09 is effective for annual reporting periods, and interim periods within those periods, beginning after December 15, 2016; however, in April 2015, the FASB issued a proposal to defer the effective date of ASU No. 2014-09 such that it would be 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 the 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.
	In April 2015, the FASB issued ASU No. 2015-05, “Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement.” ASU No. 2015-05 provides guidance to customers about whether a cloud computing arrangement includes a software license. If a cloud computing arrangement includes a software license, the customer should account for the software license element of the arrangement consistent with the acquisition of other software licenses. If a cloud computing arrangement does not include a software license, the customer should account for the arrangement as a service contract. The new guidance does not change the accounting for a customer’s accounting for service contracts. ASU No. 2015-05 is effective for interim and annual reporting periods beginning after December 15, 2015. We do not expect the adoption of ASU No. 2015-05 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	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 March 31, 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 $2.0 million and $0.5 million at March 31, 2015, and December 31, 2014, respectively, is recorded as a current derivative liability on our condensed consolidated balance sheets.
	Our outstanding warrant is 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 all of our toll manufacturing revenues are attributable to Siegfried.
	Percentages of our total revenues are as follows:
		Three months ended
		March 31,
		2015			2014
	Eisai Agreement		53.6	%		91.4	%
	Ildong Agreement		43	%		1.3	%
	Toll manufacturing agreement with Siegfried		2.8	%		6.6	%
	Other collaborative agreements		0.6	%		0.7	%
	Total percentage of revenues		100	%		100	%
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.
	Since we are in a net loss position, in addition to excluding potentially dilutive out-of-the money securities, we have excluded 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. 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
		March 31,
		2015			2014
	Stock options		15,949			14,962
	Warrant		131			679
	RSUs, PRSUs and unvested restricted stock		512			766
	Total		16,592			16,407
	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 March 31, 2015, such securities are excluded from the table above for the three months ended March 31, 2015. Because the market condition for 780,000 PRSUs issued in March 2013, was not satisfied at March 31, 2014, such securities are excluded from the table above for the three months ended March 31, 2014

Fair_Value_Disclosures_Tables

Fair Value Disclosures (Tables)	3 Months Ended
	Mar. 31, 2015
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 March 31, 2015
			Balance		Quoted Prices in		Significant Other		Significant
					Active Markets		Observable		Unobservable Inputs
					(Level 1)		Inputs		(Level 3)
							(Level 2)
	Assets:
	Money market funds1		$	208,947	$	208,947	$	0	$	0
	Liabilities:
	Warrant derivative liabilities		$	2,023	$	0	$	2,023	$	0
			Fair Value Measurements at December 31, 2014
			Balance		Quoted Prices in		Significant Other		Significant
					Active Markets		Observable		Unobservable Inputs
					(Level 1)		Inputs		(Level 3)
							(Level 2)
	Assets:
	Money market funds1		$	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)	3 Months Ended
	Mar. 31, 2015
Components of Inventory	Inventory consisted of the following, in thousands:
		March 31,		December 31,
		2015		2014
	Raw materials	$	2,247	$	1,167
	Work in process		3,937		3,520
	Finished goods at Arena GmbH		4		3,681
	Finished goods at Eisai		4,943		2,463
	Finished goods at Ildong		255		0
	Total inventory	$	11,386	$	10,831

Land_Property_and_Equipment_Ta

Land, Property and Equipment (Tables)	3 Months Ended
	Mar. 31, 2015
Land, Property and Equipment	Land, property and equipment consisted of the following, in thousands:
		March 31,			December 31,
		2015			2014
	Cost	$	176,619		$	174,938
	Less accumulated depreciation and amortization		(94,523	)		(92,019	)
	Land, property and equipment, net	$	82,096		$	82,919

Accounts_Payable_and_Other_Acc1

Accounts Payable and Other Accrued Liabilities (Tables)	3 Months Ended
	Mar. 31, 2015
Accounts Payable and Other Accrued Liabilities	Accounts payable and other accrued liabilities consisted of the following, in thousands:
		March 31,		December 31,
		2015		2014
	Accounts payable	$	1,957	$	2,844
	Accrued compensation		3,839		4,792
	Other accrued liabilities		1,328		2,573
	Total accounts payable and other accrued liabilities	$	7,124	$	10,209

Marketing_and_Supply_Agreement1

Marketing and Supply Agreement (Tables)	3 Months Ended
	Mar. 31, 2015
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
			March 31,
			2015			2014
	Net product sales		$	4,436		$	2,882
	Amortization of upfront payments			1,885			1,975
	Reimbursement of development expenses			191			745
	Milestone payment			0			500
	Reimbursement of patent and trademark expenses			60			127
	Subtotal other Eisai collaborative revenue			2,136			3,347
	Total		$	6,572		$	6,229
Deferred Revenues Attributable to Eisa	The following table summarizes the deferred revenues under our collaboration with Eisai, in thousands:
			March 31,			December 31,
			2015			2014
	Upfront payments		$	92,589		$	94,474
	Net product sales			17,806			7,081
	Total deferred revenues attributable to Eisai			110,395			101,555
	Less current portion			(25,347	)		(14,622	)
	Deferred revenues attributable to Eisai, less current portion		$	85,048		$	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	Remaining Territories
					North and South America
	BELVIQ		Not Applicable		General	Up to a total of $100.0 million -
	- Pre-approval*				Eisai: 90%; Arena: 10%	Eisai: 50%; Arena: 50%
					Certain stability work Eisai: 50%; Arena: 50%	Thereafter, Eisai: 100%
	BELVIQ		General		General	Up to a total of $50.0 million -
	- Post-approval*		Eisai: 90%; Arena 10%		Eisai: 90%; Arena: 10%	Eisai: 50%; Arena: 50%
			Non-FDA required portion of CVOT		Certain stability work	Thereafter, Eisai: 90%;
			Up to $80.0 million -		Eisai: 50%; Arena: 50%	Arena: 10%
			Eisai: 50%; Arena: 50%
			Thereafter, Eisai: 100%
			Certain pediatric studies
			Eisai: 50%; Arena: 50%
	Lorcaserin		Up to a total of $250.0 million (as reduced by up to $80.0 million for non-FDA required portion of CVOT)
	products other than		-Eisai: 50%; Arena: 50%
	BELVIQ
	- Pre-approval
	Lorcaserin		Up to a total of $100.0 million in the aggregate across all additional products -
	products other than		Eisai: 50%; Arena: 50%
	BELVIQ		Thereafter, Eisai: 90%; Arena: 10%
	- Post-approval
	*	Development required by a regulatory authority, with the exception of the non-FDA required portions of the CVOT.

Sharebased_Activity_Tables

Share-based Activity (Tables)	3 Months Ended
	Mar. 31, 2015
Share Based Compensation Expense	We recognized share-based compensation expense as follows, in thousands:
		Three months ended
		March 31,
		2015			2014
	Research and development	$	2,056		$	1,781
	General and administrative		1,777			1,420
	Total share-based compensation expense	$	3,833		$	3,201
	Total share-based compensation expense capitalized into inventory	$	62		$	0
Summary of Stock Option Activity	The following table summarizes our stock option activity during the three months ended March 31, 2015, in thousands (except per share data):
		Options			Weighted-
					Average
					Exercise Price
	Outstanding at January 1, 2015		15,831		$	5.25
	Granted		2,999			4.48
	Exercised		(603	)		2.05
	Forfeited/cancelled/expired		(493	)		6.3
	Outstanding at March 31, 2015		17,734		$	5.2
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 three months ended March 31, 2015, in thousands (except per share data):
		RSUs			Weighted-
					Average
					Grant-Date
					Fair Value
	Unvested at January 1, 2015		456		$	5.72
	Granted		0
	Vested		(44	)		6.5
	Forfeited/cancelled		0
	Unvested at March 31, 2015		412		$	5.64
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	$	4.5

Concentrations_of_Credit_Risk_1

Concentrations of Credit Risk and Major Customers (Tables)	3 Months Ended
	Mar. 31, 2015
Percentages of Total Revenues	Percentages of our total revenues are as follows:
		Three months ended
		March 31,
		2015			2014
	Eisai Agreement		53.6	%		91.4	%
	Ildong Agreement		43	%		1.3	%
	Toll manufacturing agreement with Siegfried		2.8	%		6.6	%
	Other collaborative agreements		0.6	%		0.7	%
	Total percentage of revenues		100	%		100	%

Net_Loss_Per_Share_Tables

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2015
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
		March 31,
		2015		2014
	Stock options		15,949		14,962
	Warrant		131		679
	RSUs, PRSUs and unvested restricted stock		512		766
	Total		16,592		16,407

Financial_Assets_and_Liabiliti

Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (Fair Value Measurements, Recurring, USD $)	Mar. 31, 2015		Dec. 31, 2014
In Thousands, unless otherwise specified
Assets:
Money market funds	$208,947	[1]	$143,913	[1]
Liabilities:
Warrant derivative liabilities	2,023		474
Quoted Prices in Active Markets (Level 1)
Assets:
Money market funds	208,947	[1]	143,913	[1]
Liabilities:
Warrant derivative liabilities	0		0
Significant Other Observable Inputs (Level 2)
Assets:
Money market funds	0	[1]	0	[1]
Liabilities:
Warrant derivative liabilities	2,023		474
Significant Unobservable Inputs (Level 3)
Assets:
Money market funds	0	[1]	0	[1]
Liabilities:
Warrant derivative liabilities	$0		$0
[1]	Included in cash and cash equivalents on our condensed consolidated balance sheets.

Components_of_Inventory_Detail

Components of Inventory (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Inventory [Line Items]
Raw materials	$2,247	$1,167
Work in process	3,937	3,520
Total inventory	11,386	10,831	[1]
Arena GmbH
Inventory [Line Items]
Finished goods	4	3,681
Eisai
Inventory [Line Items]
Finished goods	4,943	2,463
lldong
Inventory [Line Items]
Finished goods	$255	$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_De

Land, Property and Equipment (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]
Cost	$176,619	$174,938
Less accumulated depreciation and amortization	-94,523	-92,019
Land, property and equipment, net	$82,096	$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_Acc2

Accounts Payable and Other Accrued Liabilities (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Accounts Payable and Accrued Liabilities, Current [Abstract]
Accounts payable	$1,957	$2,844
Accrued compensation	3,839	4,792
Other accrued liabilities	1,328	2,573
Total accounts payable and other accrued liabilities	$7,124	$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_Additio

Derivative Liabilities - Additional Information (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014		Aug. 31, 2008
In Thousands, except Share data, unless otherwise specified
Derivative [Line Items]
Issuance of warrant to purchase stock, number of shares				1,106,344
Original exercise price of warrant				$7.71
Revised exercise price of warrant	$4.34
Warrant outstanding	1,965,418
Adjustment price of warrant in anti-dilution provision	$6.72
Derivative liabilities, current	$2,023	$474	[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.

Marketing_and_Supply_Agreement2

Marketing and Supply Agreement with Eisai - Additional Information (Detail) (USD $)	3 Months Ended		1 Months Ended				57 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	31-May-15	Nov. 30, 2013	Jul. 31, 2010	31-May-12	Mar. 31, 2015	Dec. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales	$6,618,000	$2,882,000
Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Recognized milestone revenue	0	500,000
Net product sales	4,436,000	2,882,000
Payable to Eisai	22,472,000						22,472,000	23,705,000	[1]
Product Purchase Price | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales	4,000,000
Voucher Redemption | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales	400,000
Scenario, Forecast | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expected payment to collaborator minimum			10,000,000
Expected payment to collaborator maximum			11,000,000
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
Aggregate one-time purchase price adjustments	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
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
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
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
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.

Revenues_Recognized_under_Coll

Revenues Recognized under Collaboration with Eisai (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales	$6,618,000	$2,882,000
Total revenues	12,256,000	6,814,000
Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales	4,436,000	2,882,000
Amortization of upfront payments	1,885,000	1,975,000
Milestone payment	0	500,000
Subtotal other Eisai collaborative revenue	2,136,000	3,347,000
Total revenues	6,572,000	6,229,000
Eisai | Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement revenue	191,000	745,000
Eisai | Patent and trademark expenses
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement revenue	$60,000	$127,000

Deferred_Revenues_under_Collab

Deferred Revenues under Collaboration with Eisai (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Thousands, unless otherwise specified
Deferred Revenue Arrangement [Line Items]
Less current portion	($26,291)	($15,238)	[1]
Deferred revenues, less current portion	91,035	93,064	[1]
Eisai
Deferred Revenue Arrangement [Line Items]
Total deferred revenues	110,395	101,555
Less current portion	-25,347	-14,622
Deferred revenues, less current portion	85,048	86,933
Eisai | Up-front Payment Arrangement
Deferred Revenue Arrangement [Line Items]
Total deferred revenues	92,589	94,474
Eisai | Net Product Sales
Deferred Revenue Arrangement [Line Items]
Total deferred revenues	$17,806	$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.

Summary_of_Cost_Sharing_Alloca

Summary of Cost Sharing Allocation (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015
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	[1]
Portion of expenses	50.00%	[1]
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%	[1]
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%	[1]
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	[1]
Portion of expenses	50.00%	[1]
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%	[1]
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%	[1]
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%	[1]
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%	[1]
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%	[1]
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%	[1]
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%	[1]
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%	[1]
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%	[1]
Belviq Product Post Approval | UNITED STATES | Arena GmbH
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	10.00%	[1]
Belviq Product Post Approval | UNITED STATES | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	90.00%	[1]
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%	[1]
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%	[1]
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%	[1]
Belviq Product Post Approval Certain Pediatric Studies | UNITED STATES | Eisai
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Portion of expenses	50.00%	[1]
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	[1]
Portion of expenses	50.00%	[1]
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%	[1]
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%	[1]
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%
[1]	Development required by a regulatory authority, with the exception of the non-FDA required portions of the CVOT.

Marketing_and_Supply_Agreement3

Marketing and Supply Agreement with Ildong - Additional Information (Detail) (USD $)	3 Months Ended		1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Nov. 30, 2012
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net product sales	$6,618,000	$2,882,000
lldong
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative agreement upfront payments			5,000,000
Collaborative Agreement Revenue Recognition Period			14 years
Recognized milestone revenue	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	$2,200,000

Share_Based_Compensation_Expen

Share Based Compensation Expense (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$3,833	$3,201
Total share-based compensation expense capitalized into inventory	62	0
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	2,056	1,781
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$1,777	$1,420

Summary_of_Stock_Option_Activi

Summary of Stock Option Activity (Detail) (Stock Options, USD $)	3 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Mar. 31, 2015
Stock Options
Number of stock options
Outstanding at January 1, 2015	15,831
Granted	2,999
Exercised	-603
Forfeited/cancelled/expired	-493
Outstanding at March 31, 2015	17,734
Weighted Average Exercise Price
Outstanding at January 1, 2015	$5.25
Granted	$4.48
Exercised	$2.05
Forfeited/cancelled/expired	$6.30
Outstanding at March 31, 2015	$5.20

Summary_of_Restricted_Stock_Un

Summary of Restricted Stock Unit Awards Activity (Detail) (Restricted Stock Units (RSU), USD $)	3 Months Ended
	Mar. 31, 2015
Restricted Stock Units (RSU)
Restricted Stock Units
Unvested at January 1, 2015	456,000
Granted	0
Vested	-44,000
Forfeited/cancelled	0
Unvested at March 31, 2015	412,000
Weighted-Average Grant-Date Fair Value
Unvested at January 1, 2015	$5.72
Granted	$0
Vested	$6.50
Forfeited/cancelled	$0
Unvested at March 31, 2015	$5.64

Sharebased_Activity_Additional

Share-based Activity - Additional Information (Detail) (Performance restricted stock units, USD $)	1 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Stockholders Equity [Line Items]
Units granted	745,000	695,000	780,000
Multiplier of grant-date fair value for cap on number of PRSUs that may be granted	6
Vesting period	3 years
Cap on percentage of funding if the absolute 3-year TSR is negative	100.00%
PRSU grant-date fair value	$3.40
Aggregate intrinsic value of units outstanding	$9.70
Share Based Compensation
Stockholders Equity [Line Items]
Units granted	745,000
Minimum
Stockholders Equity [Line Items]
Number of shares to be awarded as a percentage of target amounts	0.00%
Maximum
Stockholders Equity [Line Items]
Number of shares to be awarded as a percentage of target amounts	200.00%

Assumptions_and_Estimated_Fair

Assumptions and Estimated Fair Value of Performance Restricted Stock Unit Awards (Detail) (Performance restricted stock units, USD $)	3 Months Ended
	Mar. 31, 2015
Performance restricted stock units
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

Percentages_of_Total_Revenues_

Percentages of Total Revenues (Detail) (Sales Revenue, Net)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Concentration Risk [Line Items]
Percentage of revenues	100.00%	100.00%
Eisai Agreement
Concentration Risk [Line Items]
Percentage of revenues	53.60%	91.40%
Ildong Agreement
Concentration Risk [Line Items]
Percentage of revenues	43.00%	1.30%
Toll manufacturing services agreement with Siegfried
Concentration Risk [Line Items]
Percentage of revenues	2.80%	6.60%
Other collaborative agreements
Concentration Risk [Line Items]
Percentage of revenues	0.60%	0.70%

Potentially_Dilutive_Securitie

Potentially Dilutive Securities Excluded From Calculation of Diluted Net Loss Per Share (Detail)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities excluded from calculation of diluted net loss per share	16,592	16,407
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	15,949	14,962
Warrant
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total antidilutive securities excluded from calculation of diluted net loss per share	131	679
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	512	766

Net_Loss_Per_Share_Additional_

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

Issuance_of_Common_Stock_Addit

Issuance of Common Stock - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended
In Thousands, except Share data, unless otherwise specified	Jan. 31, 2015	Mar. 31, 2015	Mar. 31, 2014
Class of Stock [Line Items]
Issuance of common stock	21,000,000
Common stock, par value	$0.00
Sale of stock, price per share	$4.81
Net proceeds from sale of common stock	$100,700	$101,979	$2,927

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (Subsequent Event, Roivant, USD $)	0 Months Ended
	11-May-15	11-May-15
Subsequent Event | Roivant
Subsequent Event [Line Items]
Expected collaborative agreement upfront payment	$4,000,000
Additional milestone payments on achievement	$41,500,000	$41,500,000