CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional paid-in capital	Accumulated other comprehensive income	Accumulated deficit
Beginning balance at Dec. 31, 2013	$ 25,885	$ 13	$ 214,756	$ 9,507	$ (198,391)
Beginning balance (in shares) at Dec. 31, 2013		13,446,976
Increase (Decrease) in Stockholders' Equity
Net loss	(43,698)				(43,698)
Stock-based compensation expense	7,050		7,050
Reclassification of warrants	36,931		36,931
Exercise of options for cash	887	$ 1	886
Exercise of options for cash (in shares)		76,224
Net exercise of warrants	$ 993		993
Net exercise of warrants (in shares)	43,526	43,526
Unrealized gain on investments	$ 14			14
Ending balance at Dec. 31, 2014	28,062	$ 14	260,616	9,521	(242,089)
Ending balance (in shares) at Dec. 31, 2014		13,566,726
Increase (Decrease) in Stockholders' Equity
Net loss	(64,544)				(64,544)
Stock-based compensation expense	10,254		10,254
Exercise of options for cash	552		552
Exercise of options for cash (in shares)		36,566
Issuance of common stock, net of costs	143,293	$ 4	143,289
Issuance of common stock, net of costs (in shares)		4,837,500
Issuance of common stock from ESPP	522		522
Issuance of common stock from ESPP purchase (in shares)		32,645
Net exercise of warrants	$ 0	$ 1	(1)
Net exercise of warrants (in shares)	809,498	809,498
Unrealized gain on investments	$ 37			37
Ending balance at Dec. 31, 2015	$ 118,176	$ 19	415,232	9,558	(306,633)
Ending balance (in shares) at Dec. 31, 2015	19,282,935	19,282,935
Increase (Decrease) in Stockholders' Equity
Net loss	$ (83,118)				(83,118)
Stock-based compensation expense	10,624		10,624
Exercise of options for cash	$ 240		240
Exercise of options for cash (in shares)	22,132	22,132
Issuance of common stock from ESPP	$ 297		297
Issuance of common stock from ESPP purchase (in shares)		28,483
Net exercise of warrants	$ 0
Net exercise of warrants (in shares)	603,545	289,789
Exercise of warrants for cash	$ 2,115	$ 1	2,114
Exercise of warrants for cash (in shares)	313,756	313,756
Unrealized gain on investments	$ (25)			(25)
Ending balance at Dec. 31, 2016	$ 48,309	$ 20	$ 428,507	$ 9,533	$ (389,751)
Ending balance (in shares) at Dec. 31, 2016	19,937,095	19,937,095