STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital Common Stock	Additional Paid-in Capital Warrants	Accumulated Deficit	Series 1 Preferred Stock - Mezzanine
Beginning Balance (in shares) at Dec. 31, 2013		100,159,618
Beginning Balance at Dec. 31, 2013	$ 49,383	$ 100	$ 386,511	$ 3,603	$ (340,831)
Stock-based compensation	$ 4,743		4,743
Exercise of warrants to purchase common stock (in shares)	3,725,277	3,747,254
Exercise of warrants to purchase common stock	$ 10,654	$ 4	13,963	(3,313)
Exercise of employee stock options (in shares)	613,138	613,138
Exercise of employee stock options	$ 1,386		1,386
Issuance of restricted common stock		66,828
Repurchase of shares of restricted common stock (in shares)		(112,333)
Repurchase of shares of restricted common stock	(544)		(544)
Cancelled of restricted stock		(22,400)
Expired warrants			290	(290)
Net loss	(31,781)				(31,781)
Ending Balance (in shares) at Dec. 31, 2014		104,452,105
Ending Balance at Dec. 31, 2014	33,841	$ 104	406,349	$ 0	(372,612)
Stock-based compensation	$ 7,997		7,997
Exercise of employee stock options (in shares)	3,249,160	2,519,267
Exercise of employee stock options	$ 4,568	$ 3	4,566
Issuance of restricted common stock		1,590,574
Issuance of restricted common stock		$ 2	(2)
Issuance of common stock in licensing agreement (in shares)		11,722,163
Issuance of common stock in licensing agreement	67,285	$ 12	67,273
Repurchase of shares of restricted common stock (in shares)		(61,819)
Repurchase of shares of restricted common stock	(518)		(518)
Repurchase of common stock (Shares)		(3,711)
Repurchase of common stock	(34)		(34)
Issuance of common stock, net of commissions and expenses of $6,305 (in shares)		11,500,000
Issuance of common stock, net of commissions and expenses of $6,305	94,320	$ 12	94,309
Net loss	(120,088)				(120,088)
Ending Balance (in shares) at Dec. 31, 2015		131,718,579
Ending Balance at Dec. 31, 2015	87,371	$ 132	579,939		(492,700)
Stock-based compensation	$ 8,452		8,452
Exercise of employee stock options (in shares)	234,833	189,696
Exercise of employee stock options	$ 714	$ 2	712
Issuance of restricted common stock		711,770
Issuance of restricted common stock		$ 712	(712)
Issuance of common stock in licensing agreement (in shares)						100,000
Issuance of common stock in licensing agreement	87		87			$ 118,242
Repurchase of shares of restricted common stock (in shares)		(243,207)
Repurchase of shares of restricted common stock	(1,500)	$ (2)	(1,498)
Repurchase of common stock (Shares)		(168)
Repurchase of common stock	(2)		(2)
Issuance of preferred stock dividends (in shares)						6,184
Issuance of preferred stock dividends	(7,123)		(7,123)			$ 7,079
Net loss	(165,297)				(165,297)
Ending Balance (in shares) at Dec. 31, 2016		132,376,670				106,184
Ending Balance at Dec. 31, 2016	$ (77,298)	$ 132	$ 580,567		$ (657,997)	$ 125,321