Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 96,284	$ 1,334	$ 577,721		$ (482,771)
Balance (in shares) at Dec. 31, 2017		13,343
Stock-based compensation	764		764
Unrealized loss on marketable securities	(12)			$ (12)
Net loss	(17,782)				(17,782)
Balance at Mar. 31, 2018	79,254	$ 1,334	578,485	(12)	(500,553)
Balance (in shares) at Mar. 31, 2018		13,343
Balance at Dec. 31, 2018	58,819	$ 1,334	580,771	(9)	(523,277)
Balance (in shares) at Dec. 31, 2018		13,343
Stock-based compensation	594		594
Unrealized loss on marketable securities	9			$ 9
Net loss	(10,458)				(10,458)
Balance at Mar. 31, 2019	$ 48,964	$ 1,334	$ 581,365		$ (533,735)
Balance (in shares) at Mar. 31, 2019		13,343