Intangible Assets - Goodwill and Net Carrying Amounts (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($)
Goodwill
Goodwill gross, beginning balance	$ 583,078
Accumulated impairment loss, beginning balance	(50,003)
Goodwill net, beginning balance	533,075
Acquisitions	350,965
Foreign currency translation adjustments	19,061
Goodwill gross, ending balance	953,104
Accumulated impairment loss, ending balance	(50,003)
Goodwill net, ending balance	903,101
Trade Name
Intangible Assets
Indefinite lived intangible asset, Beginning balance	619
Indefinite lived intangible asset, foreign currency translation adjustments	23
Indefinite lived intangible asset, Ending balance	642
North America Segment
Goodwill
Goodwill gross, beginning balance	452,232
Goodwill net, beginning balance	452,232
Acquisitions	103,265
Foreign currency translation adjustments	2,522
Goodwill gross, ending balance	558,019
Goodwill net, ending balance	558,019
North America Segment | Trade Name
Intangible Assets
Indefinite lived intangible asset, Beginning balance	200
Indefinite lived intangible asset, Ending balance	200
Europe & Africa Segment
Goodwill
Goodwill gross, beginning balance	130,846
Accumulated impairment loss, beginning balance	(50,003)
Goodwill net, beginning balance	80,843
Acquisitions	96,062
Foreign currency translation adjustments	8,536
Goodwill gross, ending balance	235,444
Accumulated impairment loss, ending balance	(50,003)
Goodwill net, ending balance	185,441
Europe & Africa Segment | Trade Name
Intangible Assets
Indefinite lived intangible asset, Beginning balance	419
Indefinite lived intangible asset, foreign currency translation adjustments	23
Indefinite lived intangible asset, Ending balance	442
Australia & New Zealand Segment
Goodwill
Acquisitions	151,638
Foreign currency translation adjustments	8,003
Goodwill gross, ending balance	159,641
Goodwill net, ending balance	$ 159,641