CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income including non-controlling interests	$ 72,457	$ 70,535	$ 229,367	$ 200,214
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax of ($66) and ($121) in the three and nine months ended September 30, 2019; $390 and $415 in the three and nine months ended September 30, 2018.	(348)	1,416	(320)	1,039
Defined benefit pension plan activity, net of tax of $536 and $673 in the three and nine months ended September 30, 2019; $1,278 and $1,927 in the three and nine months ended September 30, 2018.	613	3,855	2,491	5,863
Currency translation adjustment	(24,025)	(467)	(14,040)	(31,422)
Other comprehensive income (loss):	(23,760)	4,804	(11,869)	(24,520)
Comprehensive income	48,697	75,339	217,498	175,694
Comprehensive income (loss) attributable to non-controlling interests	254	(65)	234	(105)
Comprehensive income attributable to shareholders	$ 48,443	$ 75,404	$ 217,264	$ 175,799