Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income/ (Loss) [Member]
Beginning Balances at Dec. 31, 2012	$ 64,896	$ 531	$ 339,848	$ (275,509)	$ 26
Beginning 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, net of tax	(14)				(14)
Net loss	(26,624)			(26,624)
Comprehensive loss	(26,638)
Ending Balances at Dec. 31, 2013	121,710	$ 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, net of tax	(37)				(37)
Net loss	(26,417)			(26,417)
Comprehensive loss	(26,454)
Ending Balances at Dec. 31, 2014	$ 206,633	$ 690	534,518	(328,550)	(25)
Ending Balances, shares at Dec. 31, 2014	69,062,394	69,062,394
Issuance of common stock upon exercise of stock options and in connection with restricted stock units	$ 4,348	$ 12	4,336
Issuance of common stock upon exercise of stock options and in connection with restricted stock units, shares		1,164,033
Issuance of common stock under employee stock purchase plan	$ 911	$ 1	910
Issuance of common stock under employee stock purchase plan, shares	128,181	128,181
Stock-based compensation	$ 11,730		11,730
Claims settlement under Section 16(b), net of tax benefit	9,495		9,495
Comprehensive loss:
Net unrealized gain (loss) on marketable securities, net of tax	25				$ 25
Net loss	(40,703)			(40,703)
Comprehensive loss	(40,678)
Ending Balances at Dec. 31, 2015	$ 192,439	$ 703	$ 560,989	$ (369,253)
Ending Balances, shares at Dec. 31, 2015	70,354,608	70,354,608