Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2013		23,285,549
Beginning balance, value at Dec. 31, 2013	$ 66,976	$ 23	$ 162,021	$ 0	$ (95,068)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock purchase rights (in shares)		10,941
Issuance of common stock upon exercise of stock purchase rights	119		119
Exercise of stock options (in shares)		579,083
Exercise of stock options	9	$ 1	8
Vesting of restricted stock (in shares)		143,004
Vesting of restricted stock	0
Stock-based compensation	9,178		9,178
Unrealized gain/(loss) on available-for-sale investments	(107)			(107)
Net loss	(48,133)				(48,133)
Ending balance (in shares) at Dec. 31, 2014		24,018,577
Ending balance, value at Dec. 31, 2014	28,042	$ 24	171,326	(107)	(143,201)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock purchase rights (in shares)		5,029
Issuance of common stock upon exercise of stock purchase rights	96		96
Exercise of stock options (in shares)		296,716
Exercise of stock options	1,282		1,282
Issuance of common stock upon net exercise of warrants (in shares)		314,368
Issuance of common stock upon net exercise of warrants	9		9
Vesting of restricted stock (in shares)		69,249
Vesting of restricted stock	0
Stock-based compensation	12,945		12,945
Excess tax benefit	463		463
Unrealized gain/(loss) on available-for-sale investments	(72)			(72)
Net loss	(74,363)				(74,363)
Proceeds from issuance of common stock, net of commissions and expenses (in shares)		1,754,556
Proceeds from issuance of common stock	50,373	$ 2	50,371
Ending balance (in shares) at Dec. 31, 2015		26,458,495
Ending balance, value at Dec. 31, 2015	18,775	$ 26	236,492	(179)	(217,564)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock purchase rights (in shares)		75,205
Issuance of common stock upon exercise of stock purchase rights	$ 1,120		1,120
Exercise of stock options (in shares)	166,295	149,186
Exercise of stock options	$ 591		591
Vesting of restricted stock (in shares)		54,192
Vesting of restricted stock	(153)		(153)
Stock-based compensation	16,794		16,794
Unrealized gain/(loss) on available-for-sale investments	111			111
Net loss	(99,059)				(99,059)
Proceeds from issuance of common stock, net of commissions and expenses (in shares)		6,721,529
Proceeds from issuance of common stock	167,165	$ 7	167,158
Ending balance (in shares) at Dec. 31, 2016		33,458,607
Ending balance, value at Dec. 31, 2016	$ 105,344	$ 33	$ 422,002	$ (68)	$ (316,623)