CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net earnings	$ 107,223	$ 166,626	$ 241,686
Other comprehensive income (loss), net of tax:
Change in minimum liability for pension plans, net of tax effects of $238, $48 and $477, respectively	1,271	102	661
Fair value adjustment on interest rate swap contracts	187	(16)	(602)
Realized gain reclassified to earnings	(494)
Gain/Loss on held-for-sale securities	(4)
Foreign currency translation adjustments	51,631	(40,911)	(61,776)
Total other comprehensive income (loss)	52,591	(40,825)	(61,717)
Comprehensive income	$ 159,814	$ 125,801	$ 179,969