Intangible Assets - Goodwill and Net Carrying Amounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill
Goodwill gross, beginning balance	$ 949,936	$ 939,185
Accumulated impairment loss, beginning balance	(197,344)	(190,041)
Goodwill net, beginning balance	752,592	749,144
Foreign currency translation adjustments	6,510	10,751
Goodwill gross, ending balance	956,446	949,936
Accumulated impairment loss, ending balance	(197,344)	(197,344)
Goodwill net, ending balance	759,102	752,592
North America
Goodwill
Goodwill gross, beginning balance	561,513	556,570
Accumulated impairment loss, beginning balance	(7,303)	0
Goodwill net, beginning balance	554,210	556,570
Foreign currency translation adjustments	2,221	4,943
Goodwill gross, ending balance	563,734	561,513
Accumulated impairment loss, ending balance	(7,303)	(7,303)
Goodwill net, ending balance	556,431	554,210
Europe & Africa
Goodwill
Goodwill gross, beginning balance	236,992	231,121
Accumulated impairment loss, beginning balance	(50,003)	(50,003)
Goodwill net, beginning balance	186,989	181,118
Foreign currency translation adjustments	3,159	5,871
Goodwill gross, ending balance	240,151	236,992
Accumulated impairment loss, ending balance	(50,003)	(50,003)
Goodwill net, ending balance	190,148	186,989
Australia & New Zealand
Goodwill
Goodwill gross, beginning balance	151,431	151,494
Accumulated impairment loss, beginning balance	(140,038)	(140,038)
Goodwill net, beginning balance	11,393	11,456
Foreign currency translation adjustments	1,130	(63)
Goodwill gross, ending balance	152,561	151,431
Accumulated impairment loss, ending balance	(140,038)	(140,038)
Goodwill net, ending balance	$ 12,523	$ 11,393