Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings (Deficit) [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2019	$ 449,175	$ 1,404	$ 123,294	$ 561,680	$ (237,203)
Beginning Balance, Shares at Dec. 31, 2019		116,481,442			23,893,484
Net income	42,402			42,402
Employee stock plans	299		299
Employee stock plans, Shares		32,772
Shares withheld for taxes on awards	(3,856)		(3,856)
Shares withheld for taxes on awards, Shares		(76,284)
Stock-based compensation	2,775		2,775
Stock-based compensation, Shares		152,408
Repurchases of common stock	(39,072)				$ (39,072)
Repurchases of common stock, Shares		(884,018)			884,018
Ending Balance at Mar. 31, 2020	451,723	$ 1,404	122,512	604,082	$ (276,275)
Ending Balance, Shares at Mar. 31, 2020		115,706,320			24,777,502
Beginning Balance at Dec. 31, 2019	449,175	$ 1,404	123,294	561,680	$ (237,203)
Beginning Balance, Shares at Dec. 31, 2019		116,481,442			23,893,484
Net income	132,331
Ending Balance at Sep. 30, 2020	544,064	$ 1,406	124,923	694,010	$ (276,275)
Ending Balance, Shares at Sep. 30, 2020		115,785,673			24,777,502
Beginning Balance at Mar. 31, 2020	451,723	$ 1,404	122,512	604,082	$ (276,275)
Beginning Balance, Shares at Mar. 31, 2020		115,706,320			24,777,502
Net income	47,218			47,218
Employee stock plans	391		391
Employee stock plans, Shares		16,412
Shares withheld for taxes on awards	(1,199)		(1,199)
Shares withheld for taxes on awards, Shares		(24,786)
Stock-based compensation	1,528	$ 1	1,527
Stock-based compensation, Shares		58,060
Ending Balance at Jun. 30, 2020	499,661	$ 1,405	123,231	651,300	$ (276,275)
Ending Balance, Shares at Jun. 30, 2020		115,756,006			24,777,502
Net income	42,710			42,710
Employee stock plans	390		390
Employee stock plans, Shares		6,559
Shares withheld for taxes on awards	(313)		(313)
Shares withheld for taxes on awards, Shares		(4,486)
Stock-based compensation	1,616	$ 1	1,615
Stock-based compensation, Shares		27,594
Ending Balance at Sep. 30, 2020	544,064	$ 1,406	124,923	694,010	$ (276,275)
Ending Balance, Shares at Sep. 30, 2020		115,785,673			24,777,502
Beginning Balance at Dec. 31, 2020	588,531	$ 1,406	126,087	737,311	$ (276,273)
Beginning Balance, Shares at Dec. 31, 2020		115,799,503			24,777,502
Net income	48,545			48,545
Employee stock plans	460		460
Employee stock plans, Shares		28,286
Shares withheld for taxes on awards	(4,045)		(4,045)
Shares withheld for taxes on awards, Shares		(38,212)
Stock-based compensation	2,176		2,176
Stock-based compensation, Shares		76,094
Repurchases of common stock	(45,523)				$ (45,523)
Repurchases of common stock, Shares		(504,275)			504,275
Ending Balance at Mar. 31, 2021	590,143	$ 1,406	124,678	785,855	$ (321,796)
Ending Balance, Shares at Mar. 31, 2021		115,361,396			25,281,777
Beginning Balance at Dec. 31, 2020	588,531	$ 1,406	126,087	737,311	$ (276,273)
Beginning Balance, Shares at Dec. 31, 2020		115,799,503			24,777,502
Net income	183,705
Ending Balance at Sep. 30, 2021	720,809	$ 1,407	126,956	921,016	$ (328,570)
Ending Balance, Shares at Sep. 30, 2021		115,349,226			25,354,216
Beginning Balance at Mar. 31, 2021	590,143	$ 1,406	124,678	785,855	$ (321,796)
Beginning Balance, Shares at Mar. 31, 2021		115,361,396			25,281,777
Net income	61,366			61,366
Employee stock plans	400		400
Employee stock plans, Shares		20,341
Shares withheld for taxes on awards	(1,446)		(1,446)
Shares withheld for taxes on awards, Shares		(13,491)
Stock-based compensation	2,133	$ 1	2,132
Stock-based compensation, Shares		17,210
Repurchases of common stock	(3,820)				$ (3,820)
Repurchases of common stock, Shares		(40,751)			40,751
Ending Balance at Jun. 30, 2021	648,776	$ 1,407	125,764	847,221	$ (325,616)
Ending Balance, Shares at Jun. 30, 2021		115,344,705			25,322,528
Net income	73,795			73,795
Employee stock plans	464		464
Employee stock plans, Shares		36,590
Shares withheld for taxes on awards	(1,159)		(1,159)
Shares withheld for taxes on awards, Shares		(10,946)
Stock-based compensation	1,887	$ 0	1,887
Stock-based compensation, Shares		10,565
Repurchases of common stock	(2,954)				$ (2,954)
Repurchases of common stock, Shares		(31,688)			31,688
Ending Balance at Sep. 30, 2021	$ 720,809	$ 1,407	$ 126,956	$ 921,016	$ (328,570)
Ending Balance, Shares at Sep. 30, 2021		115,349,226			25,354,216