Unaudited Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]
Beginning balance, value at Dec. 31, 2019	$ 526,628	$ 613	$ 257,501	$ 576,166	$ (307,652)
Beginning balance, shares at Dec. 31, 2019		61,350			3,689
Vesting of restricted stock		$ 1	(1)
Vesting of restricted stock, shares		2
Stock-based compensation	18,313		18,313
Repurchases of common stock	(8,168)				$ (8,168)
Repurchases of common stock, shares					41
Net income	63,015			63,015
Ending balance, value at Mar. 31, 2020	599,788	$ 614	275,813	639,181	$ (315,820)
Ending balance, shares at Mar. 31, 2020		61,352			3,730
Beginning balance, value at Dec. 31, 2019	526,628	$ 613	257,501	576,166	$ (307,652)
Beginning balance, shares at Dec. 31, 2019		61,350			3,689
Net income	119,086
Ending balance, value at Sep. 30, 2020	632,399	$ 616	322,321	695,252	$ (385,790)
Ending balance, shares at Sep. 30, 2020		61,639			4,034
Beginning balance, value at Mar. 31, 2020	599,788	$ 614	275,813	639,181	$ (315,820)
Beginning balance, shares at Mar. 31, 2020		61,352			3,730
Vesting of restricted stock		$ 2	(2)
Vesting of restricted stock, shares		261
Stock-based compensation	24,597		24,597
Repurchases of common stock	(67,121)				$ (67,121)
Repurchases of common stock, shares					295
Net income	28,589			28,589
Ending balance, value at Jun. 30, 2020	585,853	$ 616	300,408	667,770	$ (382,941)
Ending balance, shares at Jun. 30, 2020		61,613			4,025
Vesting of restricted stock, shares		26
Stock-based compensation	21,913		21,913
Repurchases of common stock	(2,849)				$ (2,849)
Repurchases of common stock, shares					9
Net income	27,482			27,482
Ending balance, value at Sep. 30, 2020	632,399	$ 616	322,321	695,252	$ (385,790)
Ending balance, shares at Sep. 30, 2020		61,639			4,034
Beginning balance, value at Dec. 31, 2020	655,643	$ 618	357,908	719,619	$ (422,502)
Beginning balance, shares at Dec. 31, 2020		61,861			4,122
Vesting of restricted stock, shares		3
Stock-based compensation	25,594		25,594
Repurchases of common stock	(377)				$ (377)
Repurchases of common stock, shares					1
Net income	64,616			64,616
Ending balance, value at Mar. 31, 2021	745,476	$ 618	383,502	784,235	$ (422,879)
Ending balance, shares at Mar. 31, 2021		61,864			4,123
Beginning balance, value at Dec. 31, 2020	655,643	$ 618	357,908	719,619	$ (422,502)
Beginning balance, shares at Dec. 31, 2020		61,861			4,122
Net income	147,273
Ending balance, value at Sep. 30, 2021	825,341	$ 622	441,479	866,892	$ (483,652)
Ending balance, shares at Sep. 30, 2021		62,275			4,278
Beginning balance, value at Mar. 31, 2021	745,476	$ 618	383,502	784,235	$ (422,879)
Beginning balance, shares at Mar. 31, 2021		61,864			4,123
Vesting of restricted stock		$ 3	(3)
Vesting of restricted stock, shares		271
Stock-based compensation	26,480		26,480
Repurchases of common stock	(31,978)				$ (31,978)
Repurchases of common stock, shares					94
Net income	52,278			52,278
Ending balance, value at Jun. 30, 2021	792,256	$ 621	409,979	836,513	$ (454,857)
Ending balance, shares at Jun. 30, 2021		62,135			4,217
Vesting of restricted stock		$ 1	(1)
Vesting of restricted stock, shares		140
Stock-based compensation	31,501		31,501
Repurchases of common stock	(28,795)				$ (28,795)
Repurchases of common stock, shares					61
Net income	30,379			30,379
Ending balance, value at Sep. 30, 2021	$ 825,341	$ 622	$ 441,479	$ 866,892	$ (483,652)
Ending balance, shares at Sep. 30, 2021		62,275			4,278