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, 2016		127,797
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock, (in shares)		807
Repurchases of common stock, (in shares)		(1,425)
Balance at end of period, (in shares) at Mar. 31, 2017		127,179
Balance at beginning of period at Dec. 31, 2016		$ 128	$ 1,022,411	$ (20,502)	$ 84,562
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock		1	(1)
Net income	$ 78,521				78,521
Repurchases of common stock		(2)			(68,295)
Stock-based compensation expense			9,857
Foreign currency translation adjustments, net of tax	4,864			4,864
Cash dividends ($.28 per share and $.24 per share)					(30,601)
Balance at end of period at Mar. 31, 2017		$ 127	1,032,267	(15,638)	64,187
Balance at beginning of period, (in shares) at Dec. 31, 2017		124,261
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock, (in shares)		514
Repurchases of common stock, (in shares)		(1,212)
Balance at end of period, (in shares) at Mar. 31, 2018		123,563
Balance at beginning of period at Dec. 31, 2017	1,105,265	$ 124	1,064,601	3,507	37,033
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock		1	(1)
Net income	96,167				96,167
Repurchases of common stock		(1)			(68,488)
Stock-based compensation expense			10,556
Foreign currency translation adjustments, net of tax	5,508			5,508
Cash dividends ($.28 per share and $.24 per share)					(34,210)
Balance at end of period at Mar. 31, 2018	$ 1,114,797	$ 124	$ 1,075,156	$ 9,015	$ 30,502