Consolidated Statement of Changes in Stockholders' Equity - 9 months ended Sep. 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	114,616				114,616
Cumulative translation adjustment and foreign currency exchange hedge, net of tax	2,061					2,061
Unrealized net gain on securities available-for-sale, net of tax	17					17
Stock-based compensation	10,989		10,989
Exercise of stock options	1,640	1	1,639
Withholding tax payments on restricted stock vesting and stock option exercises	(12,906)		(12,906)
Repurchases of common stock	(36,352)			(36,352)
Cumulative effect of change in accounting for employee share-based payments	29		80		(51)
Cash dividend on common stock	(37,199)				(37,199)
Ending Balance at Sep. 30, 2017	$ 510,908	$ 121	$ 342,113	$ (153,682)	$ 332,506	$ (10,150)