CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income including non-controlling interests	$ 58,506	$ 72,457	$ 141,074	$ 229,367
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax of $337 and $(62) in the three and nine months ended September 30, 2020; $(66) and $(121) in the three and nine months ended September 30, 2019.	639	(348)	(622)	(320)
Defined benefit pension plan activity, net of tax of $(776) and $(8,303) in the three and nine months ended September 30, 2020; $536 and $673 in the three and nine months ended September 30, 2019.	(1,304)	613	(23,731)	2,491
Currency translation adjustment	13,039	(24,025)	(43,101)	(14,040)
Other comprehensive income (loss):	12,374	(23,760)	(67,454)	(11,869)
Comprehensive income	70,880	48,697	73,620	217,498
Comprehensive income (loss) attributable to non-controlling interests	62	254	14	234
Comprehensive income attributable to shareholders	$ 70,818	$ 48,443	$ 73,606	$ 217,264