Condensed Consolidated Statements Of Equity - USD ($) $ in Thousands		Total	Common Stock [Member]	Capital Surplus [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	[1]	Retained Earnings [Member]	Treasury Stock [Member]	Noncontrolling Interests [Member]
Balance at Dec. 31, 2015		$ 1,480,056	$ 617	$ 130,369	$ (76,953)		$ 1,432,980	$ (10,302)	$ 3,345
Net income including noncontrolling interests		141,266					141,259		7
Other comprehensive income		337			337
Common stock issued under share-based compensation plans	[2]	1,492	3	498			991
Tax withholding for common stock issued under share-based compensation plans		(4,166)		(4,166)
Common stock issued under employee stock purchase plan		3,583		3,583
Common stock dividends		(14,598)					(14,741)
Common stock dividends, accrued dividend shares				143
Repurchase of common stock		(29,028)	(6)	(29,022)
Distributions to noncontrolling interests		(2,050)							(2,050)
Share-based compensation expense		7,000		7,000
Balance at Sep. 30, 2016		1,583,892	614	108,405	(76,616)		1,560,489	(10,302)	1,302
Balance at Dec. 31, 2016		1,537,942	606	52,219	(101,703)		1,596,269	(10,302)	853
Net income including noncontrolling interests		173,995					173,995		0
Other comprehensive income		1,144			1,144
Common stock issued under share-based compensation plans		1	2	(1)
Tax withholding for common stock issued under share-based compensation plans		(3,376)		(3,376)
Common stock issued under employee stock purchase plan		3,459	1	3,458
Common stock dividends		(14,266)					(14,390)
Common stock dividends, accrued dividend shares				124
Repurchase of common stock		(88,599)	(10)	(55,646)			(7,774)	(25,169)
Distributions to noncontrolling interests		0							0
Share-based compensation expense		7,565		7,565
Balance at Sep. 30, 2017		$ 1,617,865	$ 599	$ 4,343	$ (100,559)		$ 1,748,100	$ (35,471)	$ 853

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

[2] Includes a $1.0 million adjustment to retained earnings to recognize net operating loss carryforwards attributable to excess tax benefits on stock compensation upon the adoption of Accounting Standards Update No. 2016-09.