Consolidated Statements of Stockholders Equity - USD ($) $ in Thousands	Total	Common Stock Shares [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balance, Shares at Dec. 31, 2017		20,210,000
Balance at Dec. 31, 2017	$ 1,198,254		$ 2,021	$ 625,568	$ 0	$ 585,624		$ (14,959)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted stock and exercise of stock options, shares issued		307,000
Issuance of restricted stock and exercise of stock options, including excess income tax benefits	14,275		28	8,090	6,157
Treasury Stock, Shares		(26,000)
Purchase of treasury stock,treasury stock acquired in lieu of cash payment on stock option exercises and income tax withholding obligations	(6,252)			0	(6,252)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	24,241			24,241
Other comprehensive income, net of tax	(1,986)							(1,986)
Net Income	28,793					28,793
Balance at Dec. 31, 2018	1,263,655		2,049	657,899	(95)	620,747	$ 6,330	(16,945)
Balance, Shares at Dec. 31, 2018		20,491,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted stock and exercise of stock options, shares issued		331,000
Issuance of restricted stock and exercise of stock options, including excess income tax benefits	7,732		25	(10,870)	18,577
Treasury Stock, Shares		(80,000)
Purchase of treasury stock,treasury stock acquired in lieu of cash payment on stock option exercises and income tax withholding obligations	(18,639)			0	(18,639)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	21,918			21,918
Other comprehensive income, net of tax	1,543							1,543
Net Income	101,035					101,035
Balance at Dec. 31, 2019	$ 1,377,244		2,074	668,947	(157)	721,782		(15,402)
Balance, Shares at Dec. 31, 2019	20,742,000	20,742,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of restricted stock and exercise of stock options, shares issued		383,000
Issuance of restricted stock and exercise of stock options, including excess income tax benefits	$ 13,193		32	167	12,994
Treasury Stock, Shares		(67,000)
Purchase of treasury stock,treasury stock acquired in lieu of cash payment on stock option exercises and income tax withholding obligations	(12,876)			0	(12,876)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	23,954			23,954
Other comprehensive income, net of tax	13,880							13,880
Net Income	86,870					86,870
Balance at Dec. 31, 2020	$ 1,502,265		$ 2,106	$ 693,068	$ (39)	$ 808,652		$ (1,522)
Balance, Shares at Dec. 31, 2020	21,058,000	21,058,000