Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Impact of Adoption	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated (Deficit)	Accumulated (Deficit) Impact of Adoption
Beginning balance (in shares) at Dec. 31, 2017			57,331,622
Beginning balance at Dec. 31, 2017	$ 213,556	$ 162,513	$ 573	$ 1,006,822		$ (793,839)	$ 162,513
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	52,271					52,271
Ending balance (in shares) at Dec. 31, 2018			57,331,622		0
Ending balance at Dec. 31, 2018	$ 428,340	$ (502)	$ 573	1,006,822	$ 0	(579,055)	$ (502)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	Impact of ASC 842
Purchase of treasury stock (in shares)					(23,952,756)
Purchase of treasury stock	$ 437,962				$ 437,962
Exercise of stock options (in shares)			111,660
Exercise of stock options	1,880		$ 1	1,879
Net income	35,504					35,504
Ending balance (in shares) at Dec. 31, 2019			57,443,282		(23,952,756)
Ending balance at Dec. 31, 2019	27,260		$ 574	1,008,701	$ (437,962)	(544,053)
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)			2,147,140		112,469
Exercise of stock options	12,815		$ 22	14,075	$ (1,282)
Reclass of stock options from liability to equity classification	37,661			37,661
Private placement (in shares)					68,857
Private placement	444			(813)	$ 1,257
Net income	149,221					149,221
Ending balance (in shares) at Dec. 31, 2020			59,590,422		(26,678,410)
Ending balance at Dec. 31, 2020	$ 196,775		$ 596	$ 1,059,624	$ (468,613)	$ (394,832)