CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income including non-controlling interests	$ 60,820	$ 55,848
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax of $334 and $431 in the three months ended March 31, 2018 and 2017	855	1,524
Defined benefit pension plan activity, net of tax of $431 and $213 in the three months ended March 31, 2018 and 2017	1,287	714
Currency translation adjustment	19,387	28,533
Other comprehensive income (loss):	21,529	30,771
Comprehensive income	82,349	86,619
Comprehensive income (loss) attributable to non-controlling interests	55	26
Comprehensive income attributable to shareholders	$ 82,294	$ 86,593