STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Stock Options	Common Stock	Common Stock Stock Options	Additional Paid-in Capital Common Stock	Additional Paid-in Capital Common Stock Stock Options	Additional Paid-in Capital Warrants	Accumulated Deficit
Beginning Balance (in shares) at Dec. 31, 2012			83,236,840
Beginning Balance at Dec. 31, 2012	$ 48,445		$ 83		$ 325,177		$ 6,909	$ (283,724)
Stock-based compensation	3,507				3,507
Issuance of common stock, net of commission and expenses of $3,678 (2013) & $6,305 (2015) (in shares)			16,445,000
Issuance of common stock, net of commission and expenses of $3,678 (2013) & $6,305 (2015)	$ 53,880		$ 16		53,864
Exercise of employee stock options (in shares)	570,168			570,168
Exercise of employee stock options		$ 956		$ 1		$ 955
Exercise of warrants to purchase common stock (in shares)	112,808		112,808
Exercise of warrants to purchase common stock	$ 200				396		(196)
Issuance of restricted common stock			75,272
Repurchase of shares of restricted common stock (in shares)			(116,723)
Repurchase of shares of restricted common stock	(498)				(498)
Cancelled/ Forfeiture of unvested restricted common stock			(163,747)
Expired warrants					3,110		(3,110)
Net loss	(57,107)							(57,107)
Ending Balance (in shares) at Dec. 31, 2013			100,159,618
Ending Balance at Dec. 31, 2013	49,383		$ 100		386,511		3,603	(340,831)
Stock-based compensation	$ 4,743				4,743
Exercise of employee stock options (in shares)	613,138			613,138
Exercise of employee stock options		1,386				1,386
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)
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/ Forfeiture of unvested restricted common 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
Issuance of common stock, net of commission and expenses of $3,678 (2013) & $6,305 (2015) (in shares)			11,500,000
Issuance of common stock, net of commission and expenses of $3,678 (2013) & $6,305 (2015)	$ 94,320		$ 12		94,309
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)
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 in licensing agreement (in shares)			11,722,163
Issuance of common stock in licensing agreement	67,285		$ 12		67,273
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)