Unaudited Condensed Consolidated Statement of Equity Statement - 9 months ended Sep. 30, 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	244,772	0	0	0	254,162	(9,547)	157
Dividends declared on common stock	93,002	0	0	0	(93,002)	0	0
Employee share-based compensation earned	11,740	0	0	11,740	0	0	0
Stock option exercises	(18,481)	(1,340)	0	(17,141)	0	0	0
Restricted stock awards, net of forfeitures	0	178	0	178	0	0	0
Purchase of Company common stock	(275,726)	0	(7,302)	(38,159)	(230,265)	0	0
Noncontrolling interest payments	80	0	0	0	0	0	80
Other	1,132	103	0	1,029	0	0	0
Balance at end of period at Sep. 30, 2018	1,488,986	$ 193,557	$ (12,623)	$ 962,041	313,720	32,167	$ 124
Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 172,232				$ 172,461	$ (229)