Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Cumulative Effect, Period of Adoption, Adjustment	Accumulated (Deficit)
Beginning balance at Dec. 31, 2019	$ 27,260		$ 574	$ 1,008,701	$ (437,962)	$ 0		$ (544,053)
Beginning balance (in shares) at Dec. 31, 2019			57,443,282		(23,952,756)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Purchase of treasury stock (in shares)					(2,682,042)
Purchase of treasury stock	(30,626)				$ (30,626)
Exercise of stock options (in shares)			26,109
Exercise of stock options	356		$ 1	355
Private placement (see Note 10) (in shares)					68,857
Private placement (see Note 10)	444			(813)	$ 1,257
Net income (loss)	39,421							39,421
Ending balance at Sep. 30, 2020	36,855		$ 575	1,008,243	$ (467,331)	0		(504,632)
Ending balance (in shares) at Sep. 30, 2020			57,469,391		(26,565,941)
Beginning balance at Jun. 30, 2020	36,500		$ 574	1,009,001	$ (468,588)	0		(504,487)
Beginning balance (in shares) at Jun. 30, 2020			57,463,943		(26,634,798)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)			5,448
Exercise of stock options	56		$ 1	55
Private placement (see Note 10) (in shares)					68,857
Private placement (see Note 10)	444			(813)	$ 1,257
Net income (loss)	(145)							(145)
Ending balance at Sep. 30, 2020	36,855		$ 575	1,008,243	$ (467,331)	0		(504,632)
Ending balance (in shares) at Sep. 30, 2020			57,469,391		(26,565,941)
Beginning balance at Dec. 31, 2020	$ 196,775	$ (8,545)	$ 596	1,059,624	$ (468,613)	0	$ (8,545)	(394,832)
Beginning balance (in shares) at Dec. 31, 2020			59,590,422		(26,678,410)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Purchase of treasury stock (in shares)	0
Exercise of stock options (in shares)			482,890
Exercise of stock options	$ (401)		$ 4	(405)
Exercise of stock warrants (in shares)			570,469
Exercise of stock warrants	13,895		$ 6	13,889
Stock compensation expense	6,232			6,232
Net income (loss)	96,489							96,489
Ending balance at Sep. 30, 2021	304,445		$ 606	1,079,340	$ (468,613)	(8,545)		(298,343)
Ending balance (in shares) at Sep. 30, 2021			60,643,781		(26,678,410)
Beginning balance at Jun. 30, 2021	$ 269,703	$ (4,100)	$ 604	1,076,124	$ (468,613)	(4,445)	$ (4,100)	(333,967)
Beginning balance (in shares) at Jun. 30, 2021			60,391,597		(26,678,410)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Purchase of treasury stock (in shares)	0
Exercise of stock options (in shares)			243,615
Exercise of stock options	$ 669		$ 2	667
Exercise of stock warrants (in shares)			8,569
Exercise of stock warrants	209			209
Stock compensation expense	2,340			2,340
Net income (loss)	35,624							35,624
Ending balance at Sep. 30, 2021	$ 304,445		$ 606	$ 1,079,340	$ (468,613)	$ (8,545)		$ (298,343)
Ending balance (in shares) at Sep. 30, 2021			60,643,781		(26,678,410)