Consolidated Statement of Shareholders' Equity Statement - USD ($) $ in Thousands	Total	Common Stock [Member]	Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]
Balances at Dec. 31, 2017	$ 544,020	$ 460	$ 823,850	$ (262,960)	$ (17,330)
Net income (loss)	83,300			83,300
Other comprehensive income	480				480
Purchase of common stock	(12,140)		(12,140)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(2,380)		(2,380)
Non-cash compensation expense	7,170		7,170
Balances at Dec. 31, 2018	620,450	460	816,500	(179,660)	(16,850)
Net income (loss)	98,620			98,620
Other comprehensive income	12,120				12,120
Purchase of common stock	(36,740)	(10)	(36,730)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(3,340)		(3,340)
Non-cash compensation expense	6,450		6,450
Impact of adoption of new accounting pronouncement	(80)			1,190	(1,270)
Balances at Dec. 31, 2019	697,480	450	782,880	(79,850)	(6,000)
Net income (loss)	(79,760)			(79,760)
Other comprehensive income	380				380
Purchase of common stock	(39,420)	(30)	(39,390)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(2,600)		(2,600)
Non-cash compensation expense	8,170	10	8,160
Balances at Dec. 31, 2020	$ 584,250	$ 430	$ 749,050	$ (159,610)	$ (5,620)