Consolidated Statement of Changes in Stockholders' Equity - 6 months ended Jun. 30, 2017 - 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, 2016	$ 468,013	$ 120	$ 342,311	$ (117,330)	$ 255,140	$ (12,228)
Net income	80,486				80,486
Cumulative translation adjustment and foreign currency exchange hedge, net of tax	960					960
Unrealized net loss on securities available-for-sale, net of tax	(10)					(10)
Stock-based compensation	7,468		7,468
Exercise of stock options	1,338	1	1,337
Withholding tax payments on restricted stock vesting and stock option exercises	(8,111)		(8,111)
Repurchases of common stock	(24,147)			(24,147)
Cumulative effect of change in accounting for employee share-based payments	29		80		(51)
Cash dividend on common stock	(24,798)				(24,798)
Ending Balance at Jun. 30, 2017	$ 501,228	$ 121	$ 343,085	$ (141,477)	$ 310,777	$ (11,278)