Summary of Significant Accounting Policies (Details) (USD $) Share data in Thousands, unless otherwise specified	3 Months Ended		12 Months Ended				12 Months Ended																12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended							12 Months Ended
	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jan. 18, 2013	Dec. 31, 2013 Computer Equipment [Member]	Dec. 31, 2013 Furniture and Fixtures [Member]	Dec. 31, 2013 Leasehold Improvements [Member]	Dec. 31, 2013 Minimum [Member] Machinery and Equipment [Member]	Dec. 31, 2013 Minimum [Member] Leasehold Improvements [Member]	Dec. 31, 2012 Minimum [Member] Leasehold Improvements [Member]	Dec. 31, 2013 Maximum [Member] Machinery and Equipment [Member]	Dec. 31, 2013 Maximum [Member] Leasehold Improvements [Member]	Dec. 31, 2012 Maximum [Member] Leasehold Improvements [Member]	Dec. 31, 2013 Money Market Funds [Member]	Dec. 31, 2012 Money Market Funds [Member]	Dec. 31, 2013 Commercial Bank [Member]	Dec. 31, 2012 Commercial Bank [Member]	Dec. 31, 2013 Restricted Stock [Member]	Dec. 31, 2012 Restricted Stock [Member]	Dec. 31, 2011 Restricted Stock [Member]	Dec. 31, 2012 Salix Agreement [Member]	Jun. 30, 2011 Salix Agreement [Member] License [Member]	Dec. 31, 2012 Salix Agreement [Member] License [Member]	Jun. 30, 2011 Salix Agreement [Member] Reimbursable Development Services [Member]	Dec. 31, 2013 Salix Agreement [Member] Reimbursable Development Services [Member]	Dec. 31, 2012 Salix Agreement [Member] Reimbursable Development Services [Member]	Dec. 31, 2011 Salix Agreement [Member] Reimbursable Development Services [Member]	Dec. 31, 2012 Salix Agreement [Member] Participation in Joint Committees [Member]	Dec. 31, 2008 Ono Agreement [Member]	Dec. 31, 2013 Ono Agreement [Member]	Dec. 31, 2013 MedImmune Agreement [Member]	Dec. 31, 2013 CytoDyn Agreement [Member]	Dec. 31, 2013 Onalta Agreement [Member]
Revenue Recognition [Abstract]
Upfront license fee, received																							$ 60,000,000		$ 58,400,000			$ 1,100,000		$ 500,000	$ 15,000,000			$ 3,500,000	$ 200,000
Upfront license fee, receivable																																	5,000,000
Deferred Revenue																												200,000
Additional license fees receivable upon achievement of development milestones																																20,000,000
Collaboration Revenue			1,595,000	8,525,000	76,764,000																			58,400,000		1,100,000	200,000	200,000	59,600,000
Shares of unvested restricted stock outstanding (in shares) [Line Items]
Shares of unvested restricted stock outstanding (in shares)																				0	28	98
Cash and Cash Equivalents [Line Items]
Cash equivalents																60,364,000	56,224,000	4,898,000	2,614,000
Accounts Receivable [Abstract]
Allowance for Doubtful Accounts Receivable, Current	7,000		7,000
Auction Rate Securities [Abstract]
Auction rate securities	2,208,000		2,208,000	3,240,000
Decrease in temporary impairment of auction rate securities			68,000
Amount of temporary impairment			192,000	260,000
Goodwill and indefinite lived in-process research and development [Abstract]
Goodwill	7,702,000		7,702,000	0
Goodwill, Acquired During Period			7,702,000
Intangible Assets Acquired During Period			32,300,000
Indefinite-Lived Intangible Assets (Excluding Goodwill)	31,360,000		31,360,000	0
Reclassification to finite lived in-process research and development			(21,000)
Impairment of Intangible Assets (Excluding Goodwill)			(919,000)	0	0
Finite-Lived Intangible Assets
Finite-Lived Intangible Assets, Gross	21,000		21,000
Finite-Lived Intangible Assets, Accumulated Amortization	2,000		2,000
Finite-Lived Intangible Assets, Net, Total	19,000		19,000
Finite-Lived Intangible Asset, Useful Life			5 years
Estimated amortization of intangible assets for succeeding five years			4,000
Fair Value Measurements [Abstract]
Contingent consideration liability	15,700,000		15,700,000	0	0	15,900,000
Period of milestone achievement - Minimum	2017		2017
Period of milestone achievement - Maximum	2022		2022
Fair Value Inputs, Discount Rate - Minimum			10.00%
Fair Value Inputs, Discount Rate - Maximum			12.50%
Minimum year of beginning cash inflows						2014
Maximum year of beginning cash inflows	2018		2018
Discount Rate - Minimum						15.00%
Discount Rate - Maximum	18.00%		18.00%
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	200,000		(200,000)	0	0
Intangible impairment charge			919,000	0	0
Other current assets	1,943,000		1,943,000	1,692,000
Restricted cash	157,000		157,000	150,000
Other Asset Impairment Charges		347,000
Estimated useful lives of fixed assets [Abstract]
Estimated useful life							3 years	5 years		5 years	8 years 6 months	8 years 6 months	7 years	10 years 9 months 18 days	10 years 9 months 18 days
Useful life description									Earlier of life of improvement or lease
Deferred Lease Liability and Incentive [Abstract]
Deferred lease incentive	115,000		115,000	115,000
Total other current liabilities	115,000		115,000	115,000
Deferred lease liability	224,000		224,000	273,000
Deferred lease incentive	690,000		690,000	805,000
Total other liabilities	914,000		914,000	1,078,000
Impairment of Long-Lived Assets [Abstract]
Impairment loss					$ 22,000
Income Taxes [Abstract]
Percentage of income tax benefit realization (in hundredths)	50.00%		50.00%