Summary of Significant Accounting Policies (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfer of assets from Level 2 into Level 1					$ 27,000,000					$ 27,000,000
Schedule of Available-for-sale Securities [Line Items]
Net gain on sale of short term investments									833,000	0	0
Securities that were in an unrealized loss position					2					2
Fair Value of securities in an unrealized loss position					12,600,000					12,600,000
Unrealized gain (loss) on investment, net of taxes									450,000	543,000	(548,000)
Amortized Cost					60,974,000					60,974,000
Gross Unrealized Gains					657,000					657,000
Gross Unrealized Losses					(207,000)					(207,000)
Estimated Fair Value					61,424,000					61,424,000
Minimum percentage of likelihood for recognition of tax benefits (in hundredths)									50.00%
Revenue Recognition [Abstract]
Cost recovery revenues from an Expanded Access Program									0	3,415,000	6,917,000
Non-refundable upfront license payment									0	1,002,000	4,000
Numerator: [Abstract]
Net income (loss) attributable to common stockholders									(41,374,000)	(68,839,000)	(6,434,000)
Denominator: [Abstract]
Weighted average common shares used in calculation of basic net income (loss) per share: (in shares)									26,545	23,348	13,250
Dilutive Securities, Effect on Basic Earnings Per Share [Abstract]
Weighted Average Number of Shares, Common Stock Subject to Repurchase or Cancellation									0	0	0
Weighted Average Number of Shares, Restricted Stock									0	0	0
Weighted Average Number of Shares, Contingently Issuable									0	0	0
Weighted average number of shares - diluted (in shares)									26,545	23,348	13,250
Net income (loss) attributable to common stockholders per share: [Abstract]
Basic and Diluted (in dollars per share)	$ (0.49)	$ (0.38)	$ (0.39)	$ (0.28)	$ (0.33)	$ (1.39)	$ (0.4)	$ (0.85)	$ (1.56)	$ (2.95)	$ (0.49)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of reportable segments									1
Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computations of diluted weighted-average shares outstanding (in shares)									330	158	158
Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computations of diluted weighted-average shares outstanding (in shares)									1,818	892	214
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computations of diluted weighted-average shares outstanding (in shares)									216	487	0
Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost					55,718,000					55,718,000
Gross Unrealized Gains					652,000					652,000
Gross Unrealized Losses					(207,000)					(207,000)
Estimated Fair Value					56,163,000					56,163,000
Government Agencies Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost					5,256,000					5,256,000
Gross Unrealized Gains					5,000					5,000
Gross Unrealized Losses					0					0
Estimated Fair Value					5,261,000					5,261,000
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	90,782,000				14,848,000				90,782,000	14,848,000
Mutual funds					56,163,000					56,163,000
Government agency bonds					5,261,000					5,261,000
Certificate of deposit	2,153,000				2,085,000				2,153,000	2,085,000
Assets, Fair Value Disclosure, Total	92,935,000				78,357,000				92,935,000	78,357,000
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	90,782,000				14,848,000				90,782,000	14,848,000
Mutual funds					56,163,000					56,163,000
Government agency bonds					0					0
Certificate of deposit	2,153,000				2,085,000				2,153,000	2,085,000
Assets, Fair Value Disclosure, Total	92,935,000				73,096,000				92,935,000	73,096,000
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Inactive Markets for Identical Assets (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0				0				0	0
Mutual funds					0					0
Government agency bonds					5,261,000					5,261,000
Certificate of deposit	0				0				0	0
Assets, Fair Value Disclosure, Total	0				5,261,000				0	5,261,000
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0				0				0	0
Mutual funds					0					0
Government agency bonds					0					0
Certificate of deposit	0				0				0	0
Assets, Fair Value Disclosure, Total	$ 0				$ 0				$ 0	$ 0
Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful live of fixed assets									3 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful live of fixed assets									7 years