Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock Voting [Member]	Additional Paid-In Capital [Member]	Treasury Stock - Common Stock Voting [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance at Dec. 31, 2019	$ 770,091	$ 122	$ 342,541	$ (153,388)	$ 591,086	$ (10,270)
Net income	74,816				74,816
Cumulative translation adjustment and foreign currency exchange hedge, net of tax	(3,859)					(3,859)
Unrealized net (loss) gain on securities available-for-sale, net of tax	(491)					(491)
Stock-based compensation	6,677		6,677
Exercise of stock options	80		80
Withholding tax payments on restricted stock vesting and stock option exercises	(21,243)		(21,243)
Repurchases of common stock	(5,415)			(5,415)
Cash dividend on common stock	(22,773)				(22,773)
Ending Balance at Mar. 31, 2020	797,883	122	328,055	(158,803)	643,129	(14,620)
Beginning Balance at Dec. 31, 2019	770,091	122	342,541	(153,388)	591,086	(10,270)
Net income	158,670
Cumulative translation adjustment and foreign currency exchange hedge, net of tax	(4,210)
Ending Balance at Jun. 30, 2020	853,484	122	327,970	(164,676)	704,219	(14,151)
Beginning Balance at Mar. 31, 2020	797,883	122	328,055	(158,803)	643,129	(14,620)
Net income	83,854				83,854
Cumulative translation adjustment and foreign currency exchange hedge, net of tax	(351)					(351)
Unrealized net (loss) gain on securities available-for-sale, net of tax	820					820
Stock-based compensation	5,791		5,791
Exercise of stock options	659		659
Withholding tax payments on restricted stock vesting and stock option exercises	(6,535)		(6,535)
Repurchases of common stock	(5,873)			(5,873)
Cash dividend on common stock	(22,764)				(22,764)
Ending Balance at Jun. 30, 2020	853,484	122	327,970	(164,676)	704,219	(14,151)
Beginning Balance at Dec. 31, 2020	955,061	123	329,742	(169,523)	799,369	(4,650)
Net income	80,457				80,457
Cumulative translation adjustment and foreign currency exchange hedge, net of tax	(1,932)					(1,932)
Stock-based compensation	7,424		7,424
Exercise of stock options	244		244
Withholding tax payments on restricted stock vesting and stock option exercises	(27,422)		(27,422)
Repurchases of common stock	(520)			(520)
Cash dividend on common stock	(25,079)				(25,079)
Ending Balance at Mar. 31, 2021	988,233	123	309,988	(170,043)	854,747	(6,582)
Beginning Balance at Dec. 31, 2020	955,061	123	329,742	(169,523)	799,369	(4,650)
Net income	147,745
Cumulative translation adjustment and foreign currency exchange hedge, net of tax	(794)
Ending Balance at Jun. 30, 2021	1,021,860	123	313,683	(183,479)	896,977	(5,444)
Beginning Balance at Mar. 31, 2021	988,233	123	309,988	(170,043)	854,747	(6,582)
Net income	67,288				67,288
Cumulative translation adjustment and foreign currency exchange hedge, net of tax	1,138					1,138
Stock-based compensation	6,134		6,134
Exercise of stock options	4,421		4,421
Withholding tax payments on restricted stock vesting and stock option exercises	(6,860)		(6,860)
Repurchases of common stock	(13,436)			(13,436)
Cash dividend on common stock	(25,058)				(25,058)
Ending Balance at Jun. 30, 2021	$ 1,021,860	$ 123	$ 313,683	$ (183,479)	$ 896,977	$ (5,444)