CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income including non-controlling interests	$ 106,111	$ 60,039	$ 223,290	$ 144,972
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax of $239 and $(95) in the three and nine months ended September 30, 2017; $50 and $54 in the three and nine months ended September 30, 2016	(684)	(175)	563	16
Defined benefit pension plan activity, net of tax of $2,170 and $2,532 in the three and nine months ended September 30, 2017; $778 and $2,821 in the three and nine months ended September 30, 2016	3,958	1,313	5,384	5,548
Currency translation adjustment	18,931	(3,030)	72,820	2,222
Other comprehensive income (loss):	22,205	(1,892)	78,767	7,786
Comprehensive income	128,316	58,147	302,057	152,758
Comprehensive income (loss) attributable to non-controlling interests	16	(16)	47	(73)
Comprehensive income attributable to shareholders	$ 128,300	$ 58,163	$ 302,010	$ 152,831