Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in-Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 260,274	$ 38	$ 609,810	$ (407)	$ (349,167)
Balance (in shares) at Dec. 31, 2017		37,611
Issuance of common stock for equity awards	414		414
Issuance of common stock for equity awards (in shares)		22
Stock-based compensation expense	3,657		3,657
Net loss	(41,569)				(41,569)
Other comprehensive income (loss)	(169)			(169)
Balance at Mar. 31, 2018	222,607	$ 38	613,881	(576)	(390,736)
Balance (in shares) at Mar. 31, 2018		37,633
Balance at Dec. 31, 2018	110,079	$ 38	628,944	(77)	(518,826)
Balance (in shares) at Dec. 31, 2018		37,946
Issuance of common stock for equity awards (in shares)		47
Stock-based compensation expense	3,853		3,853
Net loss	(41,538)				(41,538)
Other comprehensive income (loss)	182			182
Balance at Mar. 31, 2019	$ 72,576	$ 38	$ 632,797	$ 105	$ (560,364)
Balance (in shares) at Mar. 31, 2019		37,993