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 income	$ 3,279	$ 193,582	$ 175,635
Other comprehensive income (loss), net of tax
Foreign currency translation adjustments	47,363	(5,986)	(23,089)
Interest rate hedges - net change in deferred gain or loss	3,892	1,670	(1,339)
Pension plans - net change in deferred actuarial loss	(64)	(965)	1,196
Other comprehensive income (loss), net of tax	51,191	(5,281)	(23,232)
Comprehensive income	$ 54,470	$ 188,301	$ 152,403