CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income including non-controlling interests	$ 27,013	$ 85,444	$ 82,568	$ 156,910
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on derivatives designated and qualifying as cash flow hedges, net of tax of $317 and $(399) in the three and six months ended June 30, 2020; $(117) and $(60) in the three and six months ended June 30, 2019.	1,108	(301)	(1,261)	28
Defined benefit pension plan activity, net of tax of $(7,691) and $(7,527) in the three and six months ended June 30, 2020; $(90) and $137 in the three and six months ended June 30, 2019.	(23,036)	1,091	(22,427)	1,878
Currency translation adjustment	14,468	4,849	(56,140)	9,985
Other comprehensive income (loss):	(7,460)	5,639	(79,828)	11,891
Comprehensive income	19,553	91,083	2,740	168,801
Comprehensive income (loss) attributable to non-controlling interests	0	(43)	(48)	(20)
Comprehensive income attributable to shareholders	$ 19,553	$ 91,126	$ 2,788	$ 168,821