Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	COMMON STOCK	CAPITAL SURPLUS	ACCUMULATED OTHER COMPREHENSIVE INCOME	RETAINED EARNINGS
Balance at beginning of period, (in shares) at Dec. 31, 2014		135,134
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock, (in shares)		591
Repurchases of common stock, (in shares)		(3,127)
Exercises of stock options, (in shares)		54
Balance at end of period, (in shares) at Sep. 30, 2015		132,652
Balance at beginning of period at Dec. 31, 2014		$ 135	$ 928,157	$ 14,730	$ 36,836
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock		1	(1)
Repurchases of common stock		(3)			(172,736)
Stock-based compensation expense			30,540
Exercise of stock options			1,511
Tax impact of equity incentive plans			4,634
Foreign currency translation adjustments, net of tax	$ (20,957)			(20,957)
Net income	264,353				264,353
Cash dividends ($.66 per share and $.60 per share)					(80,724)
Balance at end of period at Sep. 30, 2015		$ 133	964,841	(6,227)	47,729
Balance at beginning of period, (in shares) at Dec. 31, 2015		131,156
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock, (in shares)		924
Repurchases of common stock, (in shares)		(3,201)
Exercises of stock options, (in shares)		7
Balance at end of period, (in shares) at Sep. 30, 2016		128,886
Balance at beginning of period at Dec. 31, 2015	1,003,781	$ 131	979,477	(10,294)	34,467
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock		1	(1)
Repurchases of common stock		(3)			(123,607)
Stock-based compensation expense			32,803
Exercise of stock options			223
Tax impact of equity incentive plans			(795)
Foreign currency translation adjustments, net of tax	3,055			3,055
Net income	265,601				265,601
Cash dividends ($.66 per share and $.60 per share)					(86,128)
Balance at end of period at Sep. 30, 2016	$ 1,094,930	$ 129	$ 1,011,707	$ (7,239)	$ 90,333