CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income including non-controlling interests	$ 85,444	$ 68,859	$ 156,910	$ 129,679
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax of $(117) and $(60) in the three and six months ended June 30, 2019; $(309) and $25 in the three and six months ended June 30, 2018.	(301)	(1,232)	28	(377)
Defined benefit pension plan activity, net of tax of $(90) and $137 in the three and six months ended June 30, 2019; $218 and $649 in the three and six months ended June 30, 2018.	1,091	721	1,878	2,008
Currency translation adjustment	4,849	(50,342)	9,985	(30,955)
Other comprehensive income (loss):	5,639	(50,853)	11,891	(29,324)
Comprehensive income	91,083	18,006	168,801	100,355
Comprehensive income (loss) attributable to non-controlling interests	(43)	(95)	(20)	(40)
Comprehensive income attributable to shareholders	$ 91,126	$ 18,101	$ 168,821	$ 100,395