Unaudited Condensed Consolidated Statement of Equity Statement - 6 months ended Jun. 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	169,828	0	0	0	185,227	(15,497)	98
Dividends declared on common stock	62,241	0	0	0	(62,241)	0	0
Employee share-based compensation earned	7,544	0	0	7,544	0	0	0
Stock option exercises	(7,302)	(411)	0	(6,891)	0	0	0
Restricted stock awards, net of forfeitures	0	178	0	178	0	0	0
Purchase of Company common stock	(228,866)	0	(6,066)	(31,658)	(191,142)	0	0
Other	1,161	100	0	1,061	0	0	0
Balance at end of period at Jun. 30, 2018	1,476,397	$ 192,625	$ (11,387)	$ 954,128	314,669	26,217	$ 145
Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 172,232				$ 172,461	$ (229)