Unaudited Condensed Consolidated Statement of Equity Statement - 3 months ended Mar. 31, 2018 - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Capital in Excess of Par Value	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest
Balance at beginning of period at Dec. 31, 2017	$ 1,409,437	$ 191,936	$ (5,321)	$ 970,468	$ 210,364	$ 41,943	$ 47
Stockholders' Equity [Roll Forward]
Comprehensive income	72,456	0	0	0	81,988	(9,589)	57
Dividends declared on common stock	31,348	0	0	0	(31,348)	0	0
Employee share-based compensation earned	3,699	0	0	3,699	0	0	0
Stock option exercises	(4,989)	(282)	0	(4,707)	0	0	0
Restricted stock awards, net of forfeitures	0	163	0	163	0	0	0
Purchase of Company common stock	(118,797)	0	(3,095)	(16,101)	(99,601)	0	0
Other	(819)	47	0	(866)	0	0	0
Balance at end of period at Mar. 31, 2018	1,511,849	$ 192,428	$ (8,416)	$ 961,744	333,864	32,125	$ 104
Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 172,232				$ 172,461	$ (229)