CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income including non-controlling interests	$ 61,331	$ 31,309	$ 117,179	$ 84,933
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax of $97 and ($334) in the three and six months ended June 30, 2017; $207 and $4 in the three and six months ended June 30, 2016	(277)	(645)	1,247	191
Defined benefit pension plan activity, net of tax of $149 and $362 in the three and six months ended June 30, 2017; $1,132 and $2,043 in the three and six months ended June 30, 2016	712	2,617	1,426	4,235
Currency translation adjustment	25,356	(18,997)	53,889	5,252
Other comprehensive income (loss):	25,791	(17,025)	56,562	9,678
Comprehensive income	87,122	14,284	173,741	94,611
Comprehensive income (loss) attributable to non-controlling interests	5	(58)	31	(57)
Comprehensive income attributable to shareholders	$ 87,117	$ 14,342	$ 173,710	$ 94,668