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)		593
Repurchases of common stock, (in shares)		(1,575)
Exercises of stock options, (in shares)		48
Balance at end of period, (in shares) at Jun. 30, 2015		134,200
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		(2)			(90,892)
Stock-based compensation expense			19,688
Exercise of stock options			1,334
Tax impact of equity incentive plans			4,624
Foreign currency translation adjustments, net of tax	$ (13,579)			(13,579)
Net income	167,628				167,628
Cash dividends ($.44 per share and $.40 per share)					(53,984)
Balance at end of period at Jun. 30, 2015		$ 134	953,802	1,151	59,588
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)		935
Repurchases of common stock, (in shares)		(1,955)
Exercises of stock options, (in shares)		2
Balance at end of period, (in shares) at Jun. 30, 2016		130,138
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		(2)			(76,999)
Stock-based compensation expense			22,093
Exercise of stock options			78
Tax impact of equity incentive plans			(687)
Foreign currency translation adjustments, net of tax	3,793			3,793
Net income	175,032				175,032
Cash dividends ($.44 per share and $.40 per share)					(57,581)
Balance at end of period at Jun. 30, 2016	$ 1,069,508	$ 130	$ 1,000,960	$ (6,501)	$ 74,919