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, 2018	$ 620,450	$ 460	$ 816,500	$ (179,660)	$ (16,850)
Net income (loss)	19,090			19,090
Other comprehensive income (loss)	3,020				3,020
Purchase of common stock	(670)		(670)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(2,620)		(2,620)
Non-cash compensation expense	1,320		1,320
Impact of adoption of new accounting pronouncement	(80)			1,190	(1,270)
Balances at Mar. 31, 2019	640,510	460	814,530	(159,380)	(15,100)
Balances at Dec. 31, 2018	620,450	460	816,500	(179,660)	(16,850)
Net income (loss)	60,220
Other comprehensive income (loss)	1,670				1,670
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(3,240)
Balances at Sep. 30, 2019	662,060	450	796,310	(118,250)	(16,450)
Balances at Mar. 31, 2019	640,510	460	814,530	(159,380)	(15,100)
Net income (loss)	22,020			22,020
Other comprehensive income (loss)	(1,530)				(1,530)
Purchase of common stock	(14,750)	(10)	(14,740)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(610)		(610)
Non-cash compensation expense	1,720		1,720
Balances at Jun. 30, 2019	647,360	450	800,900	(137,360)	(16,630)
Net income (loss)	19,110			19,110
Other comprehensive income (loss)	180				180
Purchase of common stock	(5,670)		(5,670)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(10)		(10)
APIC, Share-based Payment Arrangement, Option, Increase for Cost Recognition	1,090		1,090
Balances at Sep. 30, 2019	662,060	450	796,310	(118,250)	(16,450)
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)		(4,470)
Shares surrendered upon exercise and vesting of equity awards to cover taxes	(30)		(30)
APIC, Share-based Payment Arrangement, Option, Increase for Cost Recognition	930		930
Balances at Sep. 30, 2020	$ 557,970	$ 430	$ 749,860	$ (183,300)	$ (9,020)