Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid In Capital	Accumulated Deficit
Beginning Balance at Dec. 31, 2013	$ 70,975	$ 2	$ 333,126	$ (262,153)
Beginning Balance (in shares) at Dec. 31, 2013		228,310
Issuance of restricted stock (in shares)		3,794
Issuance of common stock, net of issue costs and warrants	14,223	$ 1	14,222
Issuance of common stock, net of issue costs and warrants (in shares)		100,000
Cancellation of restricted stock (in shares)		(220)
Issuance of common stock for services, upon exercise of stock options and pursuant to an employee stock purchase plan	51		51
Issuance of common stock for services, upon exercise of stock options and pursuant to an employee stock purchase plan (in shares)		210
Non-cash stock-based compensation	2,860		2,860
Net loss	(41,145)			(41,145)
Ending Balance at Dec. 31, 2014	46,964	$ 3	350,259	(303,298)
Ending Balance (in shares) at Dec. 31, 2014		332,094
Shares issued upon reverse stock split (in shares)		34
Issuance of restricted stock (in shares)		23,791
Issuance of common stock, net of issue costs and warrants	22,446	$ 4	22,442
Issuance of common stock, net of issue costs and warrants (in shares)		428,333
Cancellation of restricted stock (in shares)		(37)
Issuance of common stock for services, upon exercise of stock options and pursuant to an employee stock purchase plan	3		3
Issuance of common stock for services, upon exercise of stock options and pursuant to an employee stock purchase plan (in shares)		38
Non-cash stock-based compensation	2,647		2,647
Issuance of common stock upon exercise of warrants	10,166	$ 2	10,164
Issuance of common stock upon exercise of warrants (in shares)		232,205
Issuance of common stock upon conversion of debt	714		714
Issuance of common stock upon conversion of debt (in shares)		8,502
Issuance of common stock upon exchange of debt	1,580	$ 1	1,579
Issuance of common stock upon exchange of debt (in shares)		55,392
Net loss	(36,194)			(36,194)
Ending Balance at Dec. 31, 2015	48,326	$ 10	387,808	(339,492)
Ending Balance (in shares) at Dec. 31, 2015		1,080,352
Shares issued upon reverse stock split (in shares)		4
Issuance of common stock under stock plans, net (in shares)		2,782
Issuance of common stock, net of issue costs and warrants	34,224	$ 25	34,199
Issuance of common stock, net of issue costs and warrants (in shares)		2,480,094
Cancellation of restricted stock (in shares)		(4)
Non-cash stock-based compensation	886		886
Issuance of common stock upon exercise of warrants	12,298	$ 26	12,272
Issuance of common stock upon exercise of warrants (in shares)		2,559,218
Issuance of common stock upon exchange of debt	10,758	$ 10	10,748
Issuance of common stock upon exchange of debt (in shares)		951,800
Net loss	(37,228)			(37,228)
Ending Balance at Dec. 31, 2016	$ 69,264	$ 71	$ 445,913	$ (376,720)
Ending Balance (in shares) at Dec. 31, 2016		7,074,246