Condensed Consolidated Statements Of Equity - USD ($) $ in Thousands		Total	Common Stock [Member]	Capital Surplus [Member]	Accumulated Other Comprehensive Loss [Member]	[1]	Retained Earnings [Member]	Treasury Stock [Member]	Noncontrolling Interests [Member]
Balance at Dec. 31, 2017		$ 1,674,117	$ 599	$ 8,005	$ (94,200)		$ 1,796,556	$ (37,693)	$ 850
Net income including noncontrolling interests		205,611					205,563		48
Other comprehensive (loss) income		884			884
Cumulative-effect adjustment	[2]	(854)					(854)
Common stock issued under share-based compensation plans		0	1	(1)
Tax withholding for common stock issued under share-based compensation plans		(3,745)		(3,745)
Common stock issued under employee stock purchase plan		4,286	1	4,285
Common stock dividends		(14,036)					(14,152)
Common stock dividends, accrued dividend shares				116
Repurchase of common stock		(95,639)						95,639
Share-based compensation expense		8,502		8,502
Balance at Sep. 30, 2018		1,779,126	601	17,162	(93,316)		1,987,113	(133,332)	898
Balance at Jun. 30, 2018		1,735,133	600	13,054	(93,600)		1,912,430	(98,201)	850
Net income including noncontrolling interests		79,421					79,373		48
Other comprehensive (loss) income		284			284
Common stock issued under employee stock purchase plan		1,528	1	1,527
Common stock dividends		(4,655)					(4,690)
Common stock dividends, accrued dividend shares				35
Repurchase of common stock		(35,131)						(35,131)
Share-based compensation expense		2,546		2,546
Balance at Sep. 30, 2018		1,779,126	601	17,162	(93,316)		1,987,113	(133,332)	898
Balance at Dec. 31, 2018		1,741,441	601	21,103	(87,662)		2,060,440	(253,937)	896
Net income including noncontrolling interests		238,216					238,216		0
Other comprehensive (loss) income		292			292
Common stock issued under share-based compensation plans		0	2	(2)
Tax withholding for common stock issued under share-based compensation plans		(3,771)		(3,771)
Common stock issued under employee stock purchase plan		4,501		4,501
Common stock dividends		(13,458)					(13,573)
Common stock dividends, accrued dividend shares				115
Distributions to noncontrolling interests		(250)							(250)
Share-based compensation expense		8,840		8,840
Balance at Sep. 30, 2019		1,975,811	603	30,786	(87,370)		2,285,083	(253,937)	646
Balance at Jun. 30, 2019		1,894,831	603	26,640	(86,896)		2,207,775	(253,937)	646
Net income including noncontrolling interests		81,834					81,834		0
Other comprehensive (loss) income		(474)			(474)
Tax withholding for common stock issued under share-based compensation plans		(36)		(36)
Common stock issued under employee stock purchase plan		1,532		1,532
Common stock dividends		(4,491)					(4,526)
Common stock dividends, accrued dividend shares				35
Share-based compensation expense		2,615		2,615
Balance at Sep. 30, 2019		$ 1,975,811	$ 603	$ 30,786	$ (87,370)		$ 2,285,083	$ (253,937)	$ 646

[1] Represents cumulative foreign currency translation adjustments and post retirement liability adjustments.

[2] Represents adjustment to retained earnings upon the adoption of Accounting Standards Codification Topic 606, “Revenue from Contracts with Customers.”