CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock Member	Additional Paid In Capital Member	Retained Earnings Member	Accumulated Other Comprehensive Loss Member	Treasury Stock Member
Beginning Balance at Dec. 31, 2016		$ 49,187	$ 129,483	$ 1,754,907	$ (291,756)	$ (350,630)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings				214,891
Other comprehensive loss, net of tax	$ 74,916				74,916
Dividends paid/declared				(24,740)
Restricted stock			(12,104)			12,105
Stock options exercised			(5,724)			19,902
Other			(2,237)	(734)		889
Share-based compensation			11,191			381
Repurchases of common stock						(52,127)
Ending Balance at Dec. 31, 2017	1,527,800	49,187	120,609	1,944,324	(216,840)	(369,480)
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2014-09 [Member]				(2,274)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	118,431			118,431
Net earnings | Accounting Standards Update 2014-09 [Member]	(2,798)
Other comprehensive loss, net of tax	(22,676)				(22,676)
Dividends paid/declared				(13,231)
Restricted stock			(6,923)			6,923
Stock options exercised			(1,535)			7,896
Other			(725)			725
Share-based compensation			7,599			201
Repurchases of common stock						(46,115)
Ending Balance at Jun. 30, 2018	$ 1,576,096	$ 49,187	$ 119,025	$ 2,047,250	$ (239,516)	$ (399,850)