CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Common stock warrants	Additional paid-in capital	Accumulated other comprehensive income	Accumulated deficit
Beginning balance at Dec. 31, 2012	$ 34,416	$ 10	$ 11,153	$ 154,224	$ 9,520	$ (140,491)
Beginning balance (in shares) at Dec. 31, 2012		9,957,725
Increase (Decrease) in Stockholders' Equity
Net loss	(52,859)					(52,859)
Stock-based compensation expense	1,823			1,823
Reclassification of warrants	(16,194)		(11,153)			(5,041)
Reclassification of stock option liability	1,369			1,369
Issuance of common stock, net of costs	54,196	$ 3		54,193
Issuance of common stock, net of costs (in shares)		3,337,500
Exercise of options for cash	540			540
Exercise of options for cash (in shares)		40,534
Exercise of warrants for cash	21			21
Exercise of warrants for cash (in shares)		2,896
Net exercise of warrants	2,586			2,586
Net exercise of warrants (in shares)		108,321
Unrealized loss on investments	(13)				(13)
Ending balance at Dec. 31, 2013	25,885	$ 13	0	214,756	9,507	(198,391)
Ending 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 loss on investments	$ 14				14
Ending balance at Dec. 31, 2014	$ 28,062	$ 14	0	260,616	9,521	(242,089)
Ending balance (in shares) at Dec. 31, 2014	13,566,726	13,566,726
Increase (Decrease) in Stockholders' Equity
Net loss	$ (64,544)					(64,544)
Stock-based compensation expense	10,254			10,254
Issuance of common stock, net of costs	143,293	$ 4		143,289
Issuance of common stock, net of costs (in shares)		4,837,500
Exercise of options for cash	$ 552	$ 0		552
Exercise of options for cash (in shares)	36,566	36,566
Net exercise of warrants	$ 0	$ 1		(1)
Net exercise of warrants (in shares)	809,498	809,498
Issuance of common stock from ESPP purchase	$ 522			522
Issuance of common stock from ESPP purchase (in shares)		32,645
Unrealized loss on investments	37				37
Ending balance at Dec. 31, 2015	$ 118,176	$ 19	$ 0	$ 415,232	$ 9,558	$ (306,633)
Ending balance (in shares) at Dec. 31, 2015	19,282,935	19,282,935