Consolidated Statement of Stockholders' Equity (Unaudited) (USD $) In Thousands	Total	Common Stock	Additional Paid-in-Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss) Unrealized Gains (Losses) on Interest Rate Swaps	Accumulated Other Comprehensive Income (Loss) Unrealized Gains (Losses) on Marketable Securities	Accumulated Other Comprehensive Income (Loss) Unrealized Gains (Losses) on Currency Translation	Treasury Stock
Beginning Balance at Dec. 31, 2010	$ 784,368	$ 261	$ 363,966	$ 519,843	$ (10,953)	$ 50	$ (7,852)	$ (80,947)
Beginning Balance, shares at Dec. 31, 2010		26,096
Comprehensive income:
Net income	40,045			40,045
Interest rate swap adjustment, net of tax provision of $188	314				314
Unrealized loss on investments, net of tax benefit of $7	(11)					(11)
Unrealized gain on currency translation	1,297						1,297
Total comprehensive income	41,645
Purchases of treasury stock	(14,009)							(14,009)
Issuance of common and treasury shares to employee benefit plans	(854)	(1)	(4,665)					3,812
Issuance of common and treasury shares to employee benefit plans, shares		(122)
Proceeds from sales of common stock under employee benefit plans	1,900	1	1,899
Proceeds from sales of common stock under employee benefit plans, Shares		49
Issuance of restricted stock		2	(2)
Issuance of restricted stock, shares		257
Forfeiture of restricted stock		(1)	1
Forfeiture of restricted stock, shares		(75)
Stock-based compensation	5,558		5,558
Tax effect from options exercised and the vesting of restricted shares	546		546
Cash dividends	(5,248)			(5,248)
Ending Balance at Jun. 30, 2011	$ 813,906	$ 262	$ 367,303	$ 554,640	$ (10,639)	$ 39	$ (6,555)	$ (91,144)
Ending Balance, shares at Jun. 30, 2011		26,205