CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Treasury Stock
Beginning balance at Dec. 31, 2018	$ (18,578)	$ 19	$ 119,724	$ (135,160)	$ (3,161)
Increase (Decrease) in Stockholders' Equity
Net (loss) income	172			172
Stock-based compensation expense	1,101		1,101
Common stock issued for stock-based awards, net	(486)		(2,309)		1,823
Exercise of Weichai Warrant	38,068	4	38,064
Ending balance at Sep. 30, 2019	20,277	23	156,580	(134,988)	(1,338)
Beginning balance at Jun. 30, 2019	14,391	23	158,530	(140,744)	(3,418)
Increase (Decrease) in Stockholders' Equity
Net (loss) income	5,756			5,756
Stock-based compensation expense	173		173
Common stock issued for stock-based awards, net	(43)		(2,123)		2,080
Ending balance at Sep. 30, 2019	20,277	23	156,580	(134,988)	(1,338)
Beginning balance at Dec. 31, 2019	28,497	23	156,727	(126,912)	(1,341)
Increase (Decrease) in Stockholders' Equity
Net (loss) income	(19,920)			(19,920)
Stock-based compensation expense	482		411		71
Common stock issued for stock-based awards, net	(23)				(23)
Ending balance at Sep. 30, 2020	9,036	23	157,138	(146,832)	(1,293)
Beginning balance at Jun. 30, 2020	10,355	23	157,052	(145,366)	(1,354)
Increase (Decrease) in Stockholders' Equity
Net (loss) income	(1,466)			(1,466)
Stock-based compensation expense	165		94		71
Common stock issued for stock-based awards, net	(18)		(8)		(10)
Ending balance at Sep. 30, 2020	$ 9,036	$ 23	$ 157,138	$ (146,832)	$ (1,293)