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, 2019	$ 697,480	$ 450	$ 782,880	$ (79,850)	$ (6,000)
Net income (loss)	13,120			13,120
Other comprehensive income (loss)	(3,680)				(3,680)
Purchase of common stock	(31,570)	(20)	(31,550)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(1,830)		(1,830)
Non-cash compensation expense	1,940		1,940
Balances at Mar. 31, 2020	675,460	430	751,440	(66,730)	(9,680)
Balances at Dec. 31, 2019	697,480	450	782,880	(79,850)	(6,000)
Net income (loss)	(103,450)
Other comprehensive income (loss)	(3,020)				(3,020)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(2,600)
Balances at Sep. 30, 2020	557,970	430	749,860	(183,300)	(9,020)
Balances at Mar. 31, 2020	675,460	430	751,440	(66,730)	(9,680)
Net income (loss)	(15,700)			(15,700)
Other comprehensive income (loss)	(660)				(660)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(740)		(740)
Non-cash compensation expense	2,740	10	2,730
Balances at Jun. 30, 2020	661,100	440	753,430	(82,430)	(10,340)
Net income (loss)	(100,870)			(100,870)
Other comprehensive income (loss)	1,320				1,320
Purchase of common stock	(4,480)	(10)	(4,470)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(30)		(30)
Non-cash compensation expense	930		930
Balances at Sep. 30, 2020	557,970	430	749,860	(183,300)	(9,020)
Balances at Dec. 31, 2020	584,250	430	749,050	(159,610)	(5,620)
Net income (loss)	13,060			13,060
Other comprehensive income (loss)	630				630
Purchase of common stock	(2,640)	0	(2,640)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(1,770)		(1,770)
Non-cash compensation expense	2,440		2,440
Balances at Mar. 31, 2021	595,970	430	747,080	(146,550)	(4,990)
Balances at Dec. 31, 2020	584,250	430	749,050	(159,610)	(5,620)
Net income (loss)	44,490
Other comprehensive income (loss)	1,110				1,110
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(4,690)
Balances at Sep. 30, 2021	614,320	430	733,520	(115,120)	(4,510)
Balances at Mar. 31, 2021	595,970	430	747,080	(146,550)	(4,990)
Net income (loss)	11,840			11,840
Other comprehensive income (loss)	990				990
Purchase of common stock	(11,570)		(11,570)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(2,850)		(2,850)
Non-cash compensation expense	3,220	0	3,220
Balances at Jun. 30, 2021	597,600	430	735,880	(134,710)	(4,000)
Net income (loss)	19,590			19,590
Other comprehensive income (loss)	(510)				(510)
Purchase of common stock	(3,950)		(3,950)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(70)		(70)
APIC, Share-based Payment Arrangement, Option, Increase for Cost Recognition	1,660		1,660
Balances at Sep. 30, 2021	$ 614,320	$ 430	$ 733,520	$ (115,120)	$ (4,510)