Intangible Assets - Goodwill and Net Carrying Amounts (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($)
Goodwill
Goodwill gross, beginning balance	$ 583,078
Accumulated impairment loss, beginning balance	(50,003)
Goodwill net, beginning balance	533,075
Acquisitions	349,974
Foreign currency translation adjustments	28,141
Impairment loss	(140,038)
Goodwill gross, ending balance	961,193
Accumulated impairment loss, ending balance	(190,041)
Goodwill net, ending balance	771,152
Trade Name
Intangible Assets
Indefinite lived intangible asset, Beginning balance	619
Indefinite lived intangible asset, foreign currency translation adjustments	37
Indefinite lived intangible asset, Ending balance	656
North America Segment
Goodwill
Goodwill gross, beginning balance	452,232
Goodwill net, beginning balance	452,232
Acquisitions	108,997
Foreign currency translation adjustments	6,869
Goodwill gross, ending balance	568,098
Goodwill net, ending balance	568,098
North America Segment | Trade Name
Intangible Assets
Indefinite lived intangible asset, Beginning balance	200
Indefinite lived intangible asset, Ending balance	200
Europe And Africa Segment
Goodwill
Goodwill gross, beginning balance	130,846
Accumulated impairment loss, beginning balance	(50,003)
Goodwill net, beginning balance	80,843
Acquisitions	98,844
Foreign currency translation adjustments	10,030
Goodwill gross, ending balance	239,720
Accumulated impairment loss, ending balance	(50,003)
Goodwill net, ending balance	189,717
Europe And Africa Segment | Trade Name
Intangible Assets
Indefinite lived intangible asset, Beginning balance	419
Indefinite lived intangible asset, foreign currency translation adjustments	37
Indefinite lived intangible asset, Ending balance	456
Australia And New Zealand Segment
Goodwill
Acquisitions	142,133
Foreign currency translation adjustments	11,242
Impairment loss	(140,038)
Goodwill gross, ending balance	153,375
Accumulated impairment loss, ending balance	(140,038)
Goodwill net, ending balance	$ 13,337