Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Subscription receivable	Additional paid-in capital	Accumulated deficit
Balance at Dec. 31, 2012	$ 24,190	$ 26	$ (2,004)	$ 81,682	$ (55,514)
Balance (shares) at Dec. 31, 2012		26,229,909
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from equity financing, net	47,118	$ 12		47,106
Proceeds from equity financing, net (in shares)		12,311,698
Subscription received	2,004		2,004
Issuance of common stock - related party	6,406	$ 2		6,404
Issuance of common stock (in shares)		1,243,781
Stock-based compensation expense	$ 1,150			1,150
Exercise of stock options (in shares)	0
Exercise of warrants	$ 352			352
Exercise of warrants (in shares)		46,837
Net loss	(31,554)				(31,554)
Balance at Dec. 31, 2013	49,666	$ 40	0	136,694	(87,068)
Balance (shares) at Dec. 31, 2013		39,832,225
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock - related party	5,154	$ 1		5,153
Issuance of common stock (in shares)		1,024,590
Stock-based compensation expense	$ 1,239			1,239
Exercise of stock options (in shares)	0
Net loss	$ (25,650)				(25,650)
Balance at Dec. 31, 2014	30,409	$ 41	0	143,086	(112,718)
Balance (shares) at Dec. 31, 2014		40,856,815
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from equity financing, net	15,872	$ 3		15,869
Proceeds from equity financing, net (in shares)		2,974,136
Stock-based compensation expense	2,038			2,038
Exercise of stock options	$ 255			255
Exercise of stock options (in shares)	56,250	56,250
Exercise of warrants	$ 82			82
Exercise of warrants (in shares)		11,584
Net loss	(34,453)				(34,453)
Balance at Dec. 31, 2015	$ 14,203	$ 44	$ 0	$ 161,330	$ (147,171)
Balance (shares) at Dec. 31, 2015		43,898,785