Arena Pharmaceuticals (ARNA) 10-Q 12 May 14 2014 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2014	6-May-14
Document Information [Line Items]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	31-Mar-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'
Trading Symbol	'ARNA	'
Entity Registrant Name	'ARENA PHARMACEUTICALS INC	'
Entity Central Index Key	'0001080709	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	219,650,003

Condensed_Consolidated_Balance

Condensed Consolidated Balance Sheets (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$203,272	$221,878	[1]
Short-term investments, available-for-sale	53,234	0	[1]
Accounts receivable	1,552	10,602	[1]
Inventory	11,947	12,759	[1]
Prepaid expenses and other current assets	6,363	3,571	[1]
Total current assets	276,368	248,810	[1]
Land, property and equipment, net	78,046	77,388	[1]
Intangibles, net	10,071	10,182	[1]
Other non-current assets	3,211	3,427	[1]
Total assets	367,696	339,807	[1]
Current liabilities:	'	'
Accounts payable and other accrued liabilities	6,806	7,317	[1]
Accrued compensation	3,285	4,205	[1]
Current portion of deferred revenues	35,393	37,861	[1]
Current portion of lease financing obligations	2,161	2,056	[1]
Total current liabilities	66,966	70,744	[1]
Deferred rent	281	247	[1]
Deferred revenues, less current portion	99,225	101,329	[1]
Derivative liabilities	5,002	4,892	[1]
Lease financing obligations, less current portion	70,167	70,738	[1]
Commitments and contingencies	'	'	[1]
Stockholders' equity:	'	'
Common stock	22	22	[1]
Additional paid-in capital	1,299,968	1,293,840	[1]
Accumulated other comprehensive income	59,053	5,728	[1]
Accumulated deficit	-1,232,988	-1,207,733	[1]
Total stockholders' equity	126,055	91,857	[1]
Total liabilities and stockholders' equity	367,696	339,807	[1]
Eisai BELVIQ Agreement	'	'
Current liabilities:	'	'
Payable to Eisai	19,321	19,305	[1]
Current portion of deferred revenues	34,839	37,301
Deferred revenues, less current portion	$93,127	$95,102
[1]	The balance sheet data at December 31, 2013, 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, 2014	Mar. 31, 2013
Revenues:	'	'
Net product sales	$2,882	$0
Manufacturing services	448	765
Total revenues	6,814	2,373
Operating Costs and Expenses:	'	'
Cost of product sales	831	473
Cost of manufacturing services	496	1,645
Research and development	20,988	14,008
General and administrative	8,037	7,251
Total operating costs and expenses	30,352	23,377
Loss from operations	-23,538	-21,004
Interest and Other Income (Expense):	'	'
Interest income	29	24
Interest expense	-1,747	-1,787
Gain (Loss) from valuation of derivative liabilities	-110	3,859
Other	111	32
Total interest and other income (expense), net	-1,717	2,128
Net loss	-25,255	-18,876
Net loss per share:	'	'
Basic	($0.12)	($0.09)
Diluted	($0.12)	($0.09)
Shares used in calculating net loss per share:	'	'
Basic	219,222	217,503
Diluted	219,222	217,503
Comprehensive Income (Loss):	'	'
Net loss	-25,255	-18,876
Foreign currency translation gain (loss)	91	-1,588
Unrealized gain on investment	53,234	0
Comprehensive income (loss)	28,070	-20,464
Eisai BELVIQ Agreement	'	'
Revenues:	'	'
Net product sales	2,882	0
Collaborative revenue	3,347	1,495
Total revenues	6,229	1,495
Other	'	'
Revenues:	'	'
Collaborative revenue	$137	$113

Condensed_Consolidated_Cash_Fl

Condensed Consolidated Cash Flow Statements (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Operating Activities	'		'
Net loss	($25,255)		($18,876)
Adjustments to reconcile net loss to net cash used in operating activities:	'		'
Depreciation and amortization	1,992		1,950
Amortization of intangibles	181		99
Share-based compensation	3,201		1,785
(Gain) Loss from valuation of derivative liabilities	110		-3,859
Amortization of prepaid financing costs	34		34
Gain on sale of equipment	-45		0
Changes in assets and liabilities:	'		'
Accounts receivable	8,934		4,013
Inventory	903		-1,300
Prepaid expenses and other assets	-2,806		-333
Accounts payable, payable to Eisai and accrued liabilities	-1,613		-810
Deferred revenues	-4,786		-954
Deferred rent	34		27
Net cash used in operating activities	-19,116		-18,224
Investing Activities	'		'
Purchases of property and equipment	-2,469		-1,266
Proceeds from sale of equipment	45		0
Other non-current assets	209		-52
Net cash used in investing activities	-2,215		-1,318
Financing Activities	'		'
Principal payments on lease financing obligations	-466		-372
Proceeds from issuance of common stock	2,927		450
Net cash provided by financing activities	2,461		78
Effect of exchange rate changes on cash	264		-377
Net decrease in cash and cash equivalents	-18,606		-19,841
Cash and cash equivalents at beginning of period	221,878	[1]	156,091
Cash and cash equivalents at end of period	$203,272		$136,250
[1]	The balance sheet data at December 31, 2013, 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, 2014
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, 2013, as filed with the Securities and Exchange Commission, or SEC, from which we derived our balance sheet as of December 31, 2013. 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.
	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, 2014
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 as of March 31, 2014, and December 31, 2013, in thousands:
			Fair Value Measurements at March 31, 2014
			Balance at		Quoted		Significant		Significant
			March 31,		Prices in		Other		Unobservable
			2014		Active		Observable		Inputs
					Markets		Inputs		(Level 3)
					(Level 1)		(Level 2)
	Assets:
	Money market funds 1		$	183,861	$	183,861	$	0	$	0
	TaiGen equity securities 2		$	53,234	$	53,234	$	0	$	0
	Liabilities:
	Warrant derivative liabilities		$	5,002	$	0	$	5,002	$	0
	1	Included in cash and cash equivalents on our condensed consolidated balance sheets.
	2	Included in short-term investments, available-for-sale on our condensed consolidated balance sheets.
			Fair Value Measurements at December 31, 2013
			Balance at		Quoted		Significant		Significant
			December 31,		Prices in		Other		Unobservable
			2013		Active		Observable		Inputs
					Markets		Inputs		(Level 3)
					(Level 1)		(Level 2)
	Assets:
	Money market funds 1		$	208,833	$	208,833	$	0	$	0
	Liabilities:
	Warrant derivative liabilities		$	4,892	$	0	$	4,892	$	0
	1	Included in cash and cash equivalents on our condensed consolidated balance sheets.

Shortterm_investments_availabl

Short-term investments, available-for-sale	3 Months Ended
	Mar. 31, 2014
Short-term investments, available-for-sale	'
	3. Short-term investments, available-for-sale
	We have held an investment in TaiGen Biotechnology Co., Ltd., or TaiGen, that, from December 31, 2011, to January 17, 2014, had a cost basis of zero due to impairment charges. On January 17, 2014, TaiGen completed an initial public offering and its common stock began to trade on the GreTai Securities Listed Market, under the name “TaiGen Biopharmaceuticals Holding Limited.” Such market is deemed to be comparable to a US over-the-counter market such that the fair value of our investment in TaiGen, which previously had been accounted for as a cost method investment with a cost basis of zero, became readily determinable. Accordingly, on January 17, 2014, we recorded our investment in TaiGen based on its fair value of approximately $49.1 million, with the unrealized gain of $49.1 million recorded as a component of accumulated other comprehensive income in the stockholders’ equity section of our condensed consolidated balance sheets. At March 31, 2014, our investment in TaiGen had a fair value of approximately $53.2 million (see Note 2). We began recording our investment in TaiGen at fair value based on the trading price of TaiGen’s common stock, and it is revalued on each balance sheet date, with any unrealized gains or losses recorded as a component of accumulated other comprehensive income (loss) in the stockholders’ equity section of our condensed consolidated balance sheets.

Inventory

Inventory	3 Months Ended
	Mar. 31, 2014
Inventory	'
	4. Inventory
	All of our inventory relates to BELVIQ, and consisted of the following as of March 31, 2014, and December 31, 2013, in thousands:
		March 31,		December 31,
		2014		2013
	Raw materials	$	692	$	657
	Work in process		4,028		4,104
	Finished goods at Arena GmbH		0		0
	Finished goods at Eisai		7,227		7,998
	Total inventory	$	11,947	$	12,759

Accounts_Payable_and_Other_Acc

Accounts Payable and Other Accrued Liabilities	3 Months Ended
	Mar. 31, 2014
Accounts Payable and Other Accrued Liabilities	'
	5. Accounts Payable and Other Accrued Liabilities
	Accounts payable and other accrued liabilities consisted of the following as of March 31, 2014, and December 31, 2013, in thousands:
		March 31,		December 31,
		2014		2013
	Accounts payable	$	2,863	$	3,721
	Accrued expenses		1,346		1,477
	Accrued clinical and preclinical study fees		2,067		1,317
	Loss provision		497		567
	Other accrued liabilities		33		235
	Total accounts payable and other accrued liabilities	$	6,806	$	7,317

Derivative_Liabilities

Derivative Liabilities	3 Months Ended
	Mar. 31, 2014
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 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. As of March 31, 2014, 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 $5.0 million and $4.9 million as of March 31, 2014, and December 31, 2013, respectively, is recorded as a long-term 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). We recognized a loss of $0.1 million in the three months ended March 31, 2014, and a gain of $3.9 million in the three months ended March 31, 2013, from revaluation of the warrants outstanding in each period.

Marketing_and_Supply_Agreement

Marketing and Supply Agreement with Eisai	3 Months Ended
	Mar. 31, 2014
Marketing and Supply Agreement with Eisai	'
	7. Marketing and Supply Agreement with Eisai
	In November 2013, Arena Pharmaceuticals GmbH, or Arena GmbH, our wholly owned subsidiary, and Eisai Inc. and Eisai Inc.’s parent company, 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 BELVIQ to all of the countries in the world, except for South Korea, Taiwan, Australia, New Zealand and Israel. BELVIQ is approved in the United States for chronic weight management in adults who are overweight with a comorbidity or obese, and it 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 provide Eisai with services related to development and regulatory activities, and manufacture and sell BELVIQ to Eisai. Under the Eisai Agreement, we received an upfront payment and are entitled to receive milestone payments based on the achievement of regulatory filings and approvals, one-time purchase price adjustment payments and other payments, and payments from sales of BELVIQ.
	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 BELVIQ 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 in the three months ended March 31, 2014, and 2013, in thousands:
			March 31,
			2014			2013
	Net product sales		$	2,882		$	0
	Amortization of upfront payments			1,975			861
	Reimbursement of research and development expenses			745			2
	Milestone payments			500			500
	Reimbursement of patent and trademark expenses			127			132
	Subtotal Eisai collaborative revenue			3,347			1,495
	Total		$	6,229		$	1,495
	The following table summarizes the deferred revenues under our collaboration with Eisai as of March 31, 2014, and December 31, 2013, in thousands:
			March 31,			December 31,
			2014			2013
	Upfront payments		$	100,130		$	102,104
	Net product sales			27,836			30,299
	Total deferred revenues attributable to Eisai			127,966			132,403
	Less current portion			(34,839	)		(37,301	)
	Deferred revenues attributable to Eisai, less current portion		$	93,127		$	95,102
	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, including $0.5 million earned in March 2014 upon Eisai filing for regulatory approval of BELVIQ in Brazil, 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 BELVIQ at our facility in Switzerland, and sell BELVIQ 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 Product Purchase Price, in the respective territory. The 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 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 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 redemption of vouchers is based on our cost of goods sold.
	In addition to payments for purchases of BELVIQ, 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 BELVIQ 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 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 BELVIQ product supply is based on Eisai’s estimated price at the time the order is shipped, which is Eisai’s estimate of the Product Purchase Price, and is subject to change on April 1 and October 1 of each year. Eisai’s estimate of the Product Purchase Price was changed as of October 1, 2013, and there was no further change as of April 1, 2014. 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 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.
	We recognized total revenues from BELVIQ net product sales of $2.9 million in the three months ended March 31, 2014, of which $2.7 million related to sales at the Product Purchase Price and $0.2 million related to redemptions of vouchers. The 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 the price that Eisai paid us did not include deductions for the use of vouchers, savings cards and deductions for certain items related to product launch. These excess payments, which reflect both the amounts Eisai has sold to date and the product supply remaining in Eisai’s inventory at March 31, 2014, are included in the $19.3 million classified as Payable to Eisai on our condensed consolidated balance sheets. On an annual basis, subsequent to the end of Eisai’s fiscal year, we will 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 patients. In addition to the FDA-required studies, we and Eisai are prioritizing the development areas of smoking cessation, a once-daily formulation, co-administration with phentermine, as well as exploring, including as part of the CVOT, BELVIQ’s effect on conversion to type 2 diabetes and improvements in cardiovascular outcomes.
	The below chart 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 BELVIQ at such party’s own expense. For example, Eisai is responsible for the expenses of the pilot study of 12-week duration to preliminarily assess BELVIQ and phentermine when co-administered.
	Eisai Second Amended and Restated Marketing and Supply Agreement: Cost Sharing for Development
			United States		Rest of	Remaining Territories
					North and South America
	BELVIQ for weight  management		Not Applicable		General	Up to total of $100.0 million -
	- Pre-approval*				Eisai: 90%; Arena: 10%	Eisai: 50%; Arena: 50%
					Certain stability work	Thereafter, Eisai: 100%
					Eisai: 50%; Arena: 50%
	BELVIQ for weight management		General - Eisai: 90%; Arena 10%		General	Up to total of $50.0 million -
	- Post-approval*				Eisai: 90%; Arena: 10%	Eisai: 50%; Arena: 50%
			Non-FDA required portion of CVOT
			Up to $80.0 million -		Certain stability work	Thereafter, Eisai: 90%;
			Eisai: 50%; Arena: 50%		Eisai: 50%; Arena: 50%	Arena: 10%
			Thereafter, Eisai: 100%
			Certain pediatric studies
			Eisai: 50%; Arena: 50%
	Products other than BELVIQ for weight management		Up to total of $250.0 million (as reduced by up to $80.0 million for non-FDA required portion of CVOT) -
	- Pre-approval		Eisai: 50%; Arena: 50%
	Products other than BELVIQ for weight management		Up to a total of $100.0 million in the aggregate across all additional products -
	- Post-approval		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, 2013, for additional information regarding termination, indemnification, product liability, certain limitations and other provisions included in the Eisai Agreement.

Sharebased_Activity

Share-based Activity	3 Months Ended
	Mar. 31, 2014
Share-based Activity	'
	8. Share-based Activity
	Share-based Compensation
	We recognized share-based compensation expense as follows, in thousands:
		Three months ended
		March 31,
		2014			2013
	Cost of product sales	$	0		$	17
	Research and development		1,781			725
	General and administrative		1,420			1,043
	Total share-based compensation expense	$	3,201		$	1,785
	Total share-based compensation expense capitalized into inventory	$	0		$	11
	Share-based Award Activity
	The following table summarizes our stock option activity during the three months ended March 31, 2014, in thousands (except per share data):
		Options			Weighted-
					Average
					Exercise Price
	Outstanding at January 1, 2014		14,681		$	4.99
	Granted		2,091			6.81
	Exercised		(594	)		4.4
	Forfeited/cancelled/expired		(10	)		10.67
	Outstanding at March 31, 2014		16,168		$	5.24
	The following table summarizes activity with respect to our time-based restricted stock unit awards, or RSUs, during the three months ended March 31, 2014, in thousands (except per share data):
		RSUs			Weighted-
					Average
					Grant-Date
					Fair Value
	Unvested at January 1, 2014		369		$	7.23
	Granted		0
	Vested		(33	)		8.81
	Forfeited/cancelled		0
	Unvested at March 31, 2014		336		$	7.07
	In the three months ended March 31, 2014, 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, 2014, of the NASDAQ Biotechnology Index. In the aggregate, the target number of shares of common stock that may be earned under the PRSUs is 695,000; 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 the 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 their grant-date fair value, which totaled $5.0 million and will be recognized over the performance period. The table below sets forth the assumptions used to value the PRSUs granted in 2014 and their estimated grant-date fair value:
	Risk-free interest rate		0.7	%
	Dividend yield		0	%
	Expected volatility		78	%
	Remaining performance period (years)		2.99
	Estimated fair value per share of PRSUs granted	$	7.16
	In the three months ended March 31, 2013, we granted our executive officers PRSUs with substantially the same terms as the PRSUs granted in 2014. In the aggregate, the target number of shares of common stock that may be earned under the 2013 PRSUs is 780,000; however, the actual number of shares that may be earned ranges from 0% to 200% of such amount. The three-year performance period for the 2013 PRSUs began March 1, 2013.
	All of the PRSUs granted to date were outstanding and unvested at March 31, 2014.

Concentration_of_Credit_Risk_a

Concentration of Credit Risk and Major Customers	3 Months Ended
	Mar. 31, 2014
Concentration of Credit Risk and Major Customers	'
	9. 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 is the exclusive distributor and our only customer for BELVIQ in the United States, which is the only jurisdiction for which BELVIQ has received regulatory approval for marketing. We also produce drug products for Siegfried AG, or Siegfried, under a manufacturing services agreement, and all of our manufacturing services revenues are attributable to Siegfried.
	Percentages of our total revenues are as follows:
		Three months ended
		March 31,
		2014			2013
	Eisai marketing and supply agreement		91.4	%		63	%
	Manufacturing services agreement with Siegfried		6.6	%		32.2	%
	Other collaborative agreements		2	%		4.8	%
	Total percentage of revenues		100	%		100	%
	Our investment in TaiGen equity securities is subject to market price volatility. See Note 3. Fluctuations in the market price of publicly traded securities may result from perceived changes in the underlying economic characteristics of the issuer, the relative price of alternative investments, general market conditions and other factors.

Net_Loss_Per_Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2014
Net Loss Per Share	'
	10. 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, we have excluded from our calculation of diluted net loss per share all potentially dilutive (i) stock options, (ii) RSUs, (iii) PRSUs, (iv) unvested restricted stock in our deferred compensation plan and (v) warrants, and our diluted net loss per share is the same as our basic net loss per share. The table below presents the 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,
		2014		2013
	Stock options		4,581		5,961
	Warrants		679		982
	RSUs and unvested restricted stock		99		82
	Total		5,359		7,025

Legal_Proceedings

Legal Proceedings	3 Months Ended
	Mar. 31, 2014
Legal Proceedings	'
	11. 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 have been 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 are seeking 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 December 30, 2011, we filed a motion to dismiss the consolidated amended complaint. On March 28, 2013, the Court granted our motion to dismiss the consolidated amended complaint without prejudice. On May 13, 2013, the lead plaintiff filed a new consolidated amended complaint. On June 14, 2013, we filed a motion to dismiss the new consolidated amended complaint. On November 5, 2013, the Court granted our motion to dismiss the new 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 now-dismissed new consolidated amended complaint. On March 20, 2014, the Court denied plaintiff’s motion for leave to amend and dismissed the consolidated amended complaint with prejudice. On April 18, 2014, the lead plaintiff filed a notice of appeal.
	In addition to the class actions, a complaint involving similar legal and factual issues has been brought by an individual stockholder. On December 30, 2011, we filed a motion to dismiss the individual stockholder’s complaint in federal court. On March 29, 2013, the Court granted our motion to dismiss, in part without prejudice. On May 13, 2013, the individual stockholder filed a new amended complaint. On June 14, 2013, we filed a motion to dismiss the new amended complaint. On March 20, 2014, the Court granted our motion to dismiss in part and remanded the remaining claims to state court.
	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.

Fair_Value_Disclosures_Tables

Fair Value Disclosures (Tables)	3 Months Ended
	Mar. 31, 2014
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 as of March 31, 2014, and December 31, 2013, in thousands:
			Fair Value Measurements at March 31, 2014
			Balance at		Quoted		Significant		Significant
			March 31,		Prices in		Other		Unobservable
			2014		Active		Observable		Inputs
					Markets		Inputs		(Level 3)
					(Level 1)		(Level 2)
	Assets:
	Money market funds 1		$	183,861	$	183,861	$	0	$	0
	TaiGen equity securities 2		$	53,234	$	53,234	$	0	$	0
	Liabilities:
	Warrant derivative liabilities		$	5,002	$	0	$	5,002	$	0
	1	Included in cash and cash equivalents on our condensed consolidated balance sheets.
	2	Included in short-term investments, available-for-sale on our condensed consolidated balance sheets.
			Fair Value Measurements at December 31, 2013
			Balance at		Quoted		Significant		Significant
			December 31,		Prices in		Other		Unobservable
			2013		Active		Observable		Inputs
					Markets		Inputs		(Level 3)
					(Level 1)		(Level 2)
	Assets:
	Money market funds 1		$	208,833	$	208,833	$	0	$	0
	Liabilities:
	Warrant derivative liabilities		$	4,892	$	0	$	4,892	$	0
	1	Included in cash and cash equivalents on our condensed consolidated balance sheets.

Inventory_Tables

Inventory (Tables)	3 Months Ended
	Mar. 31, 2014
Components of Inventory	'
	All of our inventory relates to BELVIQ, and consisted of the following as of March 31, 2014, and December 31, 2013, in thousands:
		March 31,		December 31,
		2014		2013
	Raw materials	$	692	$	657
	Work in process		4,028		4,104
	Finished goods at Arena GmbH		0		0
	Finished goods at Eisai		7,227		7,998
	Total inventory	$	11,947	$	12,759

Accounts_Payable_and_Other_Acc1

Accounts Payable and Other Accrued Liabilities (Tables)	3 Months Ended
	Mar. 31, 2014
Accounts Payable and Other Accrued Liabilities	'
	Accounts payable and other accrued liabilities consisted of the following as of March 31, 2014, and December 31, 2013, in thousands:
		March 31,		December 31,
		2014		2013
	Accounts payable	$	2,863	$	3,721
	Accrued expenses		1,346		1,477
	Accrued clinical and preclinical study fees		2,067		1,317
	Loss provision		497		567
	Other accrued liabilities		33		235
	Total accounts payable and other accrued liabilities	$	6,806	$	7,317

Marketing_and_Supply_Agreement1

Marketing and Supply Agreement with Eisai (Tables)	3 Months Ended
	Mar. 31, 2014
Revenues Recognized under Eisai Agreement	'
	The following table summarizes the revenues we recognized under our collaboration with Eisai in the three months ended March 31, 2014, and 2013, in thousands:
			March 31,
			2014			2013
	Net product sales		$	2,882		$	0
	Amortization of upfront payments			1,975			861
	Reimbursement of research and development expenses			745			2
	Milestone payments			500			500
	Reimbursement of patent and trademark expenses			127			132
	Subtotal Eisai collaborative revenue			3,347			1,495
	Total		$	6,229		$	1,495
Deferred Revenues Attributable to Eisai	'
	The following table summarizes the deferred revenues under our collaboration with Eisai as of March 31, 2014, and December 31, 2013, in thousands:
			March 31,			December 31,
			2014			2013
	Upfront payments		$	100,130		$	102,104
	Net product sales			27,836			30,299
	Total deferred revenues attributable to Eisai			127,966			132,403
	Less current portion			(34,839	)		(37,301	)
	Deferred revenues attributable to Eisai, less current portion		$	93,127		$	95,102
Summary of Cost Sharing Allocation	'
	Eisai Second Amended and Restated Marketing and Supply Agreement: Cost Sharing for Development
			United States		Rest of	Remaining Territories
					North and South America
	BELVIQ for weight  management		Not Applicable		General	Up to total of $100.0 million -
	- Pre-approval*				Eisai: 90%; Arena: 10%	Eisai: 50%; Arena: 50%
					Certain stability work	Thereafter, Eisai: 100%
					Eisai: 50%; Arena: 50%
	BELVIQ for weight management		General - Eisai: 90%; Arena 10%		General	Up to total of $50.0 million -
	- Post-approval*				Eisai: 90%; Arena: 10%	Eisai: 50%; Arena: 50%
			Non-FDA required portion of CVOT
			Up to $80.0 million -		Certain stability work	Thereafter, Eisai: 90%;
			Eisai: 50%; Arena: 50%		Eisai: 50%; Arena: 50%	Arena: 10%
			Thereafter, Eisai: 100%
			Certain pediatric studies
			Eisai: 50%; Arena: 50%
	Products other than BELVIQ for weight management		Up to total of $250.0 million (as reduced by up to $80.0 million for non-FDA required portion of CVOT) -
	- Pre-approval		Eisai: 50%; Arena: 50%
	Products other than BELVIQ for weight management		Up to a total of $100.0 million in the aggregate across all additional products -
	- Post-approval		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.

Sharebased_Activity_Tables

Share-based Activity (Tables)	3 Months Ended
	Mar. 31, 2014
Share Based Compensation Expense	'
	We recognized share-based compensation expense as follows, in thousands:
		Three months ended
		March 31,
		2014			2013
	Cost of product sales	$	0		$	17
	Research and development		1,781			725
	General and administrative		1,420			1,043
	Total share-based compensation expense	$	3,201		$	1,785
	Total share-based compensation expense capitalized into inventory	$	0		$	11
Summary of Stock Option Activity	'
	The following table summarizes our stock option activity during the three months ended March 31, 2014, in thousands (except per share data):
		Options			Weighted-
					Average
					Exercise Price
	Outstanding at January 1, 2014		14,681		$	4.99
	Granted		2,091			6.81
	Exercised		(594	)		4.4
	Forfeited/cancelled/expired		(10	)		10.67
	Outstanding at March 31, 2014		16,168		$	5.24
Summary of Restricted Stock 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, 2014, in thousands (except per share data):
		RSUs			Weighted-
					Average
					Grant-Date
					Fair Value
	Unvested at January 1, 2014		369		$	7.23
	Granted		0
	Vested		(33	)		8.81
	Forfeited/cancelled		0
	Unvested at March 31, 2014		336		$	7.07
Assumptions and Estimated Fair Value of Performance Restricted Stock Unit Awards	'
	The table below sets forth the assumptions used to value the PRSUs granted in 2014 and their estimated grant-date fair value:
	Risk-free interest rate		0.7	%
	Dividend yield		0	%
	Expected volatility		78	%
	Remaining performance period (years)		2.99
	Estimated fair value per share of PRSUs granted	$	7.16

Concentration_of_Credit_Risk_a1

Concentration of Credit Risk and Major Customers (Tables)	3 Months Ended
	Mar. 31, 2014
Percentages of Total Revenues	'
	Percentages of our total revenues are as follows:
		Three months ended
		March 31,
		2014			2013
	Eisai marketing and supply agreement		91.4	%		63	%
	Manufacturing services agreement with Siegfried		6.6	%		32.2	%
	Other collaborative agreements		2	%		4.8	%
	Total percentage of revenues		100	%		100	%

Net_Loss_Per_Share_Tables

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2014
Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share	'
	The table below presents the 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,
		2014		2013
	Stock options		4,581		5,961
	Warrants		679		982
	RSUs and unvested restricted stock		99		82
	Total		5,359		7,025

Financial_Assets_and_Liabiliti

Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)	Mar. 31, 2014		Dec. 31, 2013
In Thousands, unless otherwise specified
Liabilities:	'		'
Warrant derivative liabilities	$5,000		$4,900
Fair Value, Measurements, Recurring	'		'
Assets:	'		'
Money market funds	183,861	[1]	208,833	[1]
TaiGen equity securities	53,234	[2]	'
Liabilities:	'		'
Warrant derivative liabilities	5,002		4,892
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets (Level 1)	'		'
Assets:	'		'
Money market funds	183,861	[1]	208,833	[1]
TaiGen equity securities	53,234	[2]	'
Liabilities:	'		'
Warrant derivative liabilities	0		0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)	'		'
Assets:	'		'
Money market funds	0	[1]	0	[1]
TaiGen equity securities	0	[2]	'
Liabilities:	'		'
Warrant derivative liabilities	5,002		4,892
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)	'		'
Assets:	'		'
Money market funds	0	[1]	0	[1]
TaiGen equity securities	0	[2]	'
Liabilities:	'		'
Warrant derivative liabilities	$0		$0
[1]	Included in cash and cash equivalents on our condensed consolidated balance sheets.
[2]	Included in short-term investments, available-for-sale on our condensed consolidated balance sheets.

Recovered_Sheet1

Short-Term Investments Available-for-Sale - Additional Information (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013		Mar. 31, 2014	Jan. 17, 2014	Dec. 31, 2011
				TaiGen Biotechnology Co., Ltd.	TaiGen Biotechnology Co., Ltd.	TaiGen Biotechnology Co., Ltd.
Investment Holdings [Line Items]	'	'		'	'	'
Equity investment	'	'		'	'	$0
Investment, fair value	$53,234,000	$0	[1]	$53,234,000	$49,100,000	'
[1]	The balance sheet data at December 31, 2013, 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.

Components_of_Inventory_Detail

Components of Inventory (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Inventory [Line Items]	'	'
Raw materials	$692	$657
Work in process	4,028	4,104
Total inventory	11,947	12,759	[1]
Arena GmbH	'	'
Inventory [Line Items]	'	'
Finished goods	0	0
Eisai BELVIQ Agreement	'	'
Inventory [Line Items]	'	'
Finished goods	$7,227	$7,998
[1]	The balance sheet data at December 31, 2013, 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, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accounts Payable and Accrued Liabilities, Current [Abstract]	'	'
Accounts payable	$2,863	$3,721
Accrued expenses	1,346	1,477
Accrued clinical and preclinical study fees	2,067	1,317
Loss provision	497	567
Other accrued liabilities	33	235
Total accounts payable and other accrued liabilities	$6,806	$7,317	[1]
[1]	The balance sheet data at December 31, 2013, 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 $)	1 Months Ended	3 Months Ended
	Aug. 31, 2008	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Derivative [Line Items]	'	'	'	'
Issuance of warrant to purchase stock, number of shares	1,106,344	'	'	'
Original exercise price of warrant	7.71	'	'	'
Warrant expiration date	14-Aug-15	'	'	'
Revised exercise price of warrant	'	4.34	'	'
Warrant outstanding	'	1,965,418	'	'
Adjustment price of warrant in anti-dilution provision	$6.72	'	'	'
Fair value of warrant outstanding	'	$5,000,000	'	$4,900,000
Gain (Loss) on valuation of derivative liabilities	'	($110,000)	$3,859,000	'

Marketing_and_Supply_Agreement2

Marketing and Supply Agreement with Eisai - Additional Information (Detail) (USD $)

3 Months Ended

1 Months Ended

45 Months Ended

1 Months Ended

45 Months Ended

1 Months Ended

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2013

Nov. 30, 2013

Nov. 30, 2013

Nov. 30, 2013

Nov. 30, 2013

Mar. 31, 2014

Nov. 30, 2013

Nov. 30, 2013

Nov. 30, 2013

Nov. 30, 2013

Jul. 31, 2010

31-May-12

Mar. 31, 2014

Product Purchase Price

Voucher Redemption

Eisai BELVIQ Agreement

Eisai BELVIQ Agreement

Eisai BELVIQ Agreement

Eisai BELVIQ Agreement

Eisai BELVIQ Agreement

Eisai Second Amended Agreement

Eisai Second Amended Agreement

Eisai Second Amended Agreement

Eisai Second Amended Agreement

Eisai Second Amended Agreement

Eisai Second Amended Agreement

Original Agreement

Eisai First Amended Agreement

BELVIQ in Brazil

UNITED STATES

Non US Territories Other Than Europe, China and Japan

Europe, China and Japan

All Territories

All Non-US territories

Non-US Territories in North and South America

Territories Outside of North and South America

Eisai BELVIQ Agreement

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Collaborative agreement initiation date

'

'

'

'

'

'

'

'

'

'2013-11

'

'

'

'

'

'2010-07

'2012-05

'

Collaborative agreement upfront payments

'

'

'

'

'

'

'

'

'

$60,000,000

'

'

'

'

'

$50,000,000

$5,000,000

'

Collaborative Agreement Revenue Recognition Period

'

'

'

'

'

'

'

'

'

'15 years

'

'

'

'

'

'16 years

'15 years

'

Recognized revenues

6,814,000

2,373,000

'

'

6,229,000

1,495,000

'

'

'

'

86,500,000

'

'

'

'

'

'

500,000

Additional milestone payments on achievement

'

'

'

'

'

'

'

'

'

'

176,000,000

'

'

'

'

'

'

'

Purchase price range minimum

'

'

'

'

'

'

31.50%

30.75%

27.50%

'

'

'

'

'

'

'

'

'

Purchase price range maximum

'

'

'

'

'

'

36.50%

35.75%

35.00%

'

'

'

'

'

'

'

'

'

Annual net product sales threshold for maximum purchase price

'

'

'

'

'

'

750,000,000

750,000,000

500,000,000

'

'

'

'

'

'

'

'

'

Aggregate one-time purchase price adjustments

'

'

'

'

'

'

'

'

'

1,560,000,000

'

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

'

'

'

'

'

'

Additional one-time purchase price adjustment payments

'

'

'

'

'

'

'

'

'

'

'

'

370,000,000

185,000,000

185,000,000

'

'

'

First annual net sales threshold to earn purchase price adjustments outside of the US

'

'

'

'

'

'

'

'

'

'

'

'

'

100,000,000

100,000,000

'

'

'

Last annual net sales threshold to earn additional purchase price adjustments outside of the US

'

'

'

'

'

'

'

'

'

'

'

'

'

1,000,000,000

1,000,000,000

'

'

'

Net product sales

2,882,000

0

2,700,000

200,000

2,882,000

0

'

'

'

'

'

'

'

'

'

'

'

'

Payable to collaborators

$19,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Revenues_Recognized_under_Coll

Revenues Recognized under Collaboration with Eisai BELVIQ Agreement (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'	'
Net product sales	$2,882	$0
Total revenues	6,814	2,373
Eisai BELVIQ Agreement	'	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'	'
Net product sales	2,882	0
Amortization of upfront payments	1,975	861
Milestone payments	500	500
Subtotal Eisai collaborative revenue	3,347	1,495
Total revenues	6,229	1,495
Eisai BELVIQ Agreement | Research and development	'	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'	'
Reimbursement revenue	745	2
Eisai BELVIQ Agreement | Patents and Trademarks	'	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'	'
Reimbursement revenue	$127	$132

Deferred_Revenues_Recognized_u

Deferred Revenues Recognized under Collaboration with Eisai Agreement (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Deferred Revenue Arrangement [Line Items]	'	'
Less current portion	($35,393)	($37,861)	[1]
Deferred revenues, less current portion	99,225	101,329	[1]
Eisai BELVIQ Agreement	'	'
Deferred Revenue Arrangement [Line Items]	'	'
Total deferred revenues	127,966	132,403
Less current portion	-34,839	-37,301
Deferred revenues, less current portion	93,127	95,102
Eisai BELVIQ Agreement | Up-front Payment Arrangement	'	'
Deferred Revenue Arrangement [Line Items]	'	'
Total deferred revenues	100,130	102,104
Eisai BELVIQ Agreement | Sales Revenue, Goods, Net	'	'
Deferred Revenue Arrangement [Line Items]	'	'
Total deferred revenues	$27,836	$30,299
[1]	The balance sheet data at December 31, 2013, 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
In Millions, unless otherwise specified	Mar. 31, 2014
BELVIQ Product For Weight Management Pre Approval Up To One Hundred Million Dollars | Territories Outside of North and South America	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Aggregate expense cap on equal split of development expenses	$100	[1]
Portion of expenses	50.00%	[1]
BELVIQ Product For Weight Management Pre Approval Up To One Hundred Million Dollars | Territories Outside of North and South America | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	50.00%	[1]
BELVIQ Product For Weight Management Pre Approval More Than One Hundred Million Dollars | Territories Outside of North and South America | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	100.00%	[1]
BELVIQ Product For Weight Management Post Approval Up To Fifty Million Dollars | Territories Outside of North and South America	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Aggregate expense cap on equal split of development expenses	50	[1]
Portion of expenses	50.00%	[1]
BELVIQ Product For Weight Management Post Approval Up To Fifty Million Dollars | Territories Outside of North and South America | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	50.00%	[1]
BELVIQ Product For Weight Management Post Approval More Than Fifty Million Dollars | Territories Outside of North and South America	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	10.00%	[1]
BELVIQ Product For Weight Management Post Approval More Than Fifty Million Dollars | Territories Outside of North and South America | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	90.00%	[1]
BELVIQ Product For Weight Management Pre Approval | Non-US Territories in North and South America	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	10.00%	[1]
BELVIQ Product For Weight Management Pre Approval | Non-US Territories in North and South America | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	90.00%	[1]
BELVIQ Product For Weight Management Pre Approval Certain Stability Work | Non-US Territories in North and South America	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	50.00%	[1]
BELVIQ Product For Weight Management Pre Approval Certain Stability Work | Non-US Territories in North and South America | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	50.00%	[1]
BELVIQ Product For Weight Management Post Approval | Non-US Territories in North and South America	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	10.00%	[1]
BELVIQ Product For Weight Management Post Approval | Non-US Territories in North and South America | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	90.00%	[1]
BELVIQ Product For Weight Management Post Approval | UNITED STATES	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	10.00%	[1]
BELVIQ Product For Weight Management Post Approval | UNITED STATES | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	90.00%	[1]
BELVIQ Product For Weight Management Post Approval Certain Stability Work | Non-US Territories in North and South America	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	50.00%	[1]
BELVIQ Product For Weight Management Post Approval Certain Stability Work | Non-US Territories in North and South America | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	50.00%	[1]
BELVIQ Product for Weight Management Post Approval Certain Pediatric Studies | UNITED STATES	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	50.00%	[1]
BELVIQ Product for Weight Management Post Approval Certain Pediatric Studies | UNITED STATES | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	50.00%	[1]
BELVIQ Product For Weight Management Post Approval Non FDA Required Portion of Cardiovascular Outcomes Trial Up To Eighty Million Dollars | UNITED STATES	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Aggregate expense cap on equal split of development expenses	80	[1]
Portion of expenses	50.00%	[1]
BELVIQ Product For Weight Management Post Approval Non FDA Required Portion of Cardiovascular Outcomes Trial Up To Eighty Million Dollars | UNITED STATES | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	50.00%	[1]
BELVIQ Product For Weight Management Post Approval Non FDA Required Portion of Cardiovascular Outcomes Trial More than Eighty Million Dollars | UNITED STATES | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	100.00%	[1]
BELVIQ Product Not For Weight Management Pre-Approval	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	50.00%
BELVIQ Product Not For Weight Management Pre-Approval | Maximum	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Aggregate expense cap on equal split of development expenses	250
BELVIQ Product Not For Weight Management Pre-Approval | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	50.00%
BELVIQ Product Not For Weight Management Post-Approval Up To One Hundred Million Dollars	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Aggregate expense cap on equal split of development expenses	$100
Portion of expenses	50.00%
BELVIQ Product Not For Weight Management Post-Approval Up To One Hundred Million Dollars | Eisai BELVIQ Agreement	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	50.00%
BELVIQ Product Not For Weight Management Post-Approval More Than One Hundred Million Dollars	'
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]	'
Portion of expenses	10.00%
BELVIQ Product Not For Weight Management Post-Approval More Than One Hundred Million Dollars | Eisai BELVIQ Agreement	'
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.

Share_Based_Compensation_Expen

Share Based Compensation Expense (Detail) (USD $)	3 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Share-based compensation expense	$3,201	$1,785
Total share-based compensation expense capitalized into inventory	0	11
Cost of product sales	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Share-based compensation expense	0	17
Research and development	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Share-based compensation expense	1,781	725
General and administrative	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Share-based compensation expense	$1,420	$1,043

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, 2014
Stock Options	'
Number of stock options	'
Outstanding at January 1, 2014	14,681
Granted	2,091
Exercised	-594
Forfeited/cancelled/expired	-10
Outstanding at March 31, 2014	16,168
Weighted Average Exercise Price	'
Outstanding at January 1, 2014	$4.99
Granted	$6.81
Exercised	$4.40
Forfeited/cancelled/expired	$10.67
Outstanding at March 31, 2014	$5.24

Summary_of_Restricted_Stock_Ac

Summary of Restricted Stock Activity (Detail) (Restricted Stock Units (RSU), USD $)	3 Months Ended
	Mar. 31, 2014
Restricted Stock Units (RSU)	'
Restricted Stock Units	'
Unvested at January 1, 2014	369,000
Granted	0
Vested	-33,000
Forfeited/cancelled	0
Unvested at March 31, 2014	336,000
Weighted-Average Grant-Date Fair Value	'
Unvested at January 1, 2014	$7.23
Granted	'
Vested	$8.81
Forfeited/cancelled	'
Unvested at March 31, 2014	$7.07

ShareBased_Activity_Additional

Share-Based Activity - Additional Information (Detail) (Performance restricted stock units, USD $)	3 Months Ended
In Millions, except Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
PRSUs granted	695,000	780,000
Multipier 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	$5	'
Minimum	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Expected number of shares to be awarded as a percentage of target amounts	0.00%	0.00%
Maximum	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'
Expected number of shares to be awarded as a percentage of target amounts	200.00%	200.00%

Assumptions_used_to_Value_Perf

Assumptions used to Value Performance Restricted Stock Units Granted and Estimated Grant Date Fair Value (Detail) (Performance restricted stock units, USD $)	3 Months Ended
	Mar. 31, 2014
Performance restricted stock units	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'
Risk-free interest rate	0.70%
Dividend yield	0.00%
Expected volatility	78.00%
Remaining performance period (years)	'2 years 11 months 27 days
Estimated fair value per share of PRSUs granted	$7.16

Percentages_of_Total_Revenues_

Percentages of Total Revenues (Detail) (Revenue)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Concentration Risk [Line Items]	'	'
Percentage of revenues	100.00%	100.00%
Eisai marketing and supply agreement	'	'
Concentration Risk [Line Items]	'	'
Percentage of revenues	91.40%	63.00%
Manufacturing services agreement with Siegfried	'	'
Concentration Risk [Line Items]	'	'
Percentage of revenues	6.60%	32.20%
Other collaborative agreements	'	'
Concentration Risk [Line Items]	'	'
Percentage of revenues	2.00%	4.80%

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, 2014	Mar. 31, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'
Total antidilutive securities excluded from calculation of diluted net loss per share	5,359	7,025
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	4,581	5,961
Series B Warrants	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'
Total antidilutive securities excluded from calculation of diluted net loss per share	679	982
RSUs and Unvested Restricted Stock	'	'
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'
Total antidilutive securities excluded from calculation of diluted net loss per share	99	82