Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	COMMON STOCK	CAPITAL SURPLUS	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)	RETAINED EARNINGS
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		$ 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 ($.31 per share and $.28 per share)					(34,210)
Balance at end of period at Mar. 31, 2018		$ 124	1,075,156	9,015	30,502
Balance at beginning of period (in shares) at Dec. 31, 2018		119,078
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock (in shares)		281
Repurchases of common stock (in shares)		(1,038)
Balance at end of period (in shares) at Mar. 31, 2019		118,321
Balance at beginning of period at Dec. 31, 2018	1,063,198	$ 119	1,079,188	(16,109)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net issuances of restricted stock		0	0
Net income	109,798				109,798
Repurchases of common stock		(1)			(68,315)
Stock-based compensation expense			11,244
Foreign currency translation adjustments, net of tax	(1,897)			(1,897)
Cash dividends ($.31 per share and $.28 per share)					(36,998)
Balance at end of period at Mar. 31, 2019	$ 1,077,029	$ 118	$ 1,090,432	$ (18,006)	$ 4,485