Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock	Convertible Preferred Stock	Convertible Preferred Stock Series F Convertible Preferred Stock	Common Stock	Common Stock Redeemable Convertible Preferred Stock	Additional Paid-In Capital	Additional Paid-In Capital Redeemable Convertible Preferred Stock	Accumulated Other Comprehensive Income	Accumulated Deficit
Balance (in shares) at Dec. 31, 2014			87,405,011
Balance at Dec. 31, 2014			$ 108,877
Balance at Dec. 31, 2014	$ (109,352)						$ 6,923			$ (116,275)
Balance (in shares) at Dec. 31, 2014					24,729
Stock based compensation expense associated with vesting of stock awards	326						326
Stock options exercised for cash, value	$ 13						13
Stock options exercised for cash, shares	254				254
Conversion of convertible securities, value	$ 117,647	$ 241	$ (117,647)	$ 1,511	$ 1		117,646	$ 241
Conversion of convertible securities, shares			(94,705,256)	1,511,723	409,877	1,720
Issuance of stock, value			$ 7,259
Issuance of stock, shares			5,788,522
Conversion of preferred stock warrants to common stock warrants in connection with merger	774						774
Issuance of common stock in connection with reverse merger, value	36,537						36,537
Issuance of common stock in connection with reverse merger, shares					325,425
Unrealized (loss) gain on available-for-sale securities	1								$ 1
Net loss	(14,762)									(14,762)
Balance at Dec. 31, 2015	31,425				$ 1		162,460		1	(131,037)
Balance (in shares) at Dec. 31, 2015					762,005
Stock based compensation expense associated with vesting of stock awards	635						635
Conversion of convertible securities, value		$ 1						$ 1
Conversion of convertible securities, shares						8
Issuance of stock, value	957						957
Issuance of stock, shares					39,743
Unrealized (loss) gain on available-for-sale securities	(2)								(2)
Net loss	(16,945)									(16,945)
Balance at Dec. 31, 2016	$ 16,071				$ 1		$ 164,053		$ (1)	$ (147,982)
Balance (in shares) at Dec. 31, 2016					801,756