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, 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		$ 131	$ 979,477	$ (10,294)	$ 34,467
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock		1	(1)
Net income	$ 265,601				265,601
Repurchases of common stock		(3)			(123,607)
Stock-based compensation expense			32,803
Exercises of stock options—excess over par value			223
Tax impact of equity incentive plans			(795)
Foreign currency translation adjustments, net of tax	3,055			3,055
Cash dividends ($.72 per share and $.66 per share)					(86,128)
Balance at end of period at Sep. 30, 2016		$ 129	1,011,707	(7,239)	90,333
Balance at beginning of period, (in shares) at Dec. 31, 2016		127,797
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock, (in shares)		818
Repurchases of common stock, (in shares)		(3,268)
Exercises of stock options, (in shares)		0
Balance at end of period, (in shares) at Sep. 30, 2017		125,347
Balance at beginning of period at Dec. 31, 2016	1,086,599	$ 128	1,022,411	(20,502)	84,562
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock		1	(1)
Net income	243,537				243,537
Repurchases of common stock		(4)			(152,650)
Stock-based compensation expense			31,163
Exercises of stock options—excess over par value			0
Tax impact of equity incentive plans			0
Foreign currency translation adjustments, net of tax	22,206			22,206
Cash dividends ($.72 per share and $.66 per share)					(91,033)
Balance at end of period at Sep. 30, 2017	$ 1,139,818	$ 125	$ 1,053,573	$ 1,704	$ 84,416