Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income/ (Loss) [Member]
Beginning Balances at Dec. 31, 2011	$ 80,132us-gaap_StockholdersEquity	$ 526	$ 332,839	$ (253,245)	$ 12
Beginning Balances, shares at Dec. 31, 2011		52,554,795
Issuance of common stock upon exercise of stock options and in connection with restricted stock units	1,219	3	1,216
Issuance of common stock upon exercise of stock options and in connection with restricted stock units, shares		328,355
Issuance of common stock under employee stock purchase plan	457	2	455
Issuance of common stock under employee stock purchase plan, shares	175,375	175,375
Stock-based compensation	5,338		5,338
Comprehensive loss:
Net unrealized gain (loss) on marketable securities	14				14
Net loss	(22,264)us-gaap_NetIncomeLoss			(22,264)
Comprehensive loss	(22,250)us-gaap_ComprehensiveIncomeNetOfTax
Ending Balances at Dec. 31, 2012	64,896us-gaap_StockholdersEquity	531	339,848	(275,509)	26
Ending Balances, shares at Dec. 31, 2012		53,058,525
Issuance of common stock in connection with underwritten public offering, net of issuance costs	69,492	70	69,422
Issuance of common stock in connection with underwritten public offering, net of issuance costs, shares		7,015,000
Issuance of common stock upon exercise of stock options and in connection with restricted stock units	6,118	19	6,099
Issuance of common stock upon exercise of stock options and in connection with restricted stock units, shares		1,889,818
Issuance of common stock under employee stock purchase plan	496	1	495
Issuance of common stock under employee stock purchase plan, shares	180,551	180,551
Issuance of common stock in connection with acquisition of Ceregene, Inc.	1,200	1	1,199
Issuance of common stock in connection with acquisition of Ceregene, Inc., shares		99,998
Stock-based compensation	6,146		6,146
Comprehensive loss:
Net unrealized gain (loss) on marketable securities	(14)				(14)
Net loss	(26,624)us-gaap_NetIncomeLoss			(26,624)
Comprehensive loss	(26,638)us-gaap_ComprehensiveIncomeNetOfTax
Ending Balances at Dec. 31, 2013	121,710us-gaap_StockholdersEquity	622	423,209	(302,133)	12
Ending Balances, shares at Dec. 31, 2013		62,243,892
Issuance of common stock in connection with underwritten public offering, net of issuance costs	93,796	44	93,752
Issuance of common stock in connection with underwritten public offering, net of issuance costs, shares		4,444,444
Issuance of common stock upon exercise of stock options and in connection with restricted stock units	7,533	23	7,510
Issuance of common stock upon exercise of stock options and in connection with restricted stock units, shares		2,266,855
Issuance of common stock under employee stock purchase plan	848	1	847
Issuance of common stock under employee stock purchase plan, shares	107,203	107,203
Stock-based compensation	9,200		9,200
Comprehensive loss:
Net unrealized gain (loss) on marketable securities	(37)				(37)
Net loss	(26,417)us-gaap_NetIncomeLoss			(26,417)
Comprehensive loss	(26,454)us-gaap_ComprehensiveIncomeNetOfTax
Ending Balances at Dec. 31, 2014	$ 206,633us-gaap_StockholdersEquity	$ 690	$ 534,518	$ (328,550)	$ (25)
Ending Balances, shares at Dec. 31, 2014		69,062,394

This element represents the amount of recognized equity-based compensation during the period, that is, the amount recognized as expense in the income statement (or as asset if compensation is capitalized). Alternate captions include the words "stock-based compensation".

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