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, 2018	$ 607,878	$ 122	$ 341,860	$ (184,962)	$ 463,252	$ (12,394)
Net income	52,522				52,522
Cumulative translation adjustment and foreign currency exchange hedge, net of tax	1,118					1,118
Unrealized net (loss) gain on securities available-for-sale, net of tax	459					459
Stock-based compensation	5,196		5,196
Exercise of stock options	172		172
Withholding tax payments on restricted stock vesting and stock option exercises	(11,803)		(11,803)
Repurchases of common stock	(5,184)			(5,184)
Cash dividend on common stock	(19,212)				(19,212)
Ending Balance at Mar. 31, 2019	631,146	122	335,425	(190,146)	496,562	(10,817)
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)