CONDENSED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Gain (Loss)
Balances at Dec. 31, 2017	$ 103,797	$ 160	$ 1,089,684	$ (985,840)	$ (207)
Balances (in shares) at Dec. 31, 2017		159,877,239
Increase (Decrease) in Stockholders' Equity
Cumulative effect of accounting principle change	1,393			1,393
Net loss	(7,186)			(7,186)
Other comprehensive income (loss)	(124)				(124)
Issuance of common stock in connection with at market offering, net of issuance costs	1,553	$ 1	1,552
Issuance of common stock in connection with at market offering, net of issuance costs (in shares)		776,788
Stock-based compensation related to issuance of common stock and options in exchange for services	71		71
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)		8,308
Stock-based compensation for equity-based awards to employees and directors	1,614		1,614
401(k) contribution	10		10
Balances at Mar. 31, 2018	101,128	$ 161	1,092,931	(991,633)	(331)
Balances (in shares) at Mar. 31, 2018		160,662,335
Balances at Dec. 31, 2018	177,733	$ 186	1,189,194	(1,011,464)	(183)
Balances (in shares) at Dec. 31, 2018		186,392,682
Increase (Decrease) in Stockholders' Equity
Net loss	(10,059)			(10,059)
Other comprehensive income (loss)	282				282
Stock-based compensation related to issuance of common stock and options in exchange for services	22		22
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)		13,365
Stock-based compensation for equity-based awards to employees and directors	1,426		1,426
401(k) contribution	9		9
Balances at Mar. 31, 2019	$ 169,413	$ 186	$ 1,190,651	$ (1,021,523)	$ 99
Balances (in shares) at Mar. 31, 2019		186,406,047