Goodwill (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, Gross, Beginning Balance	$ 1,140,078	$ 826,575
Accumulated Impairment Loss, Beginning Balance	(14,482)
Goodwill, Beginning Balance	1,125,596
Goodwill acquired	15,932	335,236
Acquisition accounting adjustments	42	10,080
Goodwill impairment		(14,482)
Currency translation adjustment	45,619	(31,813)
Goodwill, Gross, Ending Balance	1,201,671	1,140,078
Accumulated Impairment Loss, Ending Balance	(14,482)	(14,482)
Goodwill, Ending Balance	1,187,189	1,125,596
North American Operations [Member]
Goodwill [Roll Forward]
Goodwill, Gross, Beginning Balance	632,937	605,234
Accumulated Impairment Loss, Beginning Balance	0
Goodwill, Beginning Balance	632,937
Goodwill acquired	4,083	26,969
Acquisition accounting adjustments	42	176
Goodwill impairment		0
Currency translation adjustment	1,690	558
Goodwill, Gross, Ending Balance	638,752	632,937
Accumulated Impairment Loss, Ending Balance	0	0
Goodwill, Ending Balance	638,752	632,937
Australian Operations [Member]
Goodwill [Roll Forward]
Goodwill, Gross, Beginning Balance	339,865	39,312
Accumulated Impairment Loss, Beginning Balance	0
Goodwill, Beginning Balance	339,865
Goodwill acquired	0	308,267
Acquisition accounting adjustments	0	168
Goodwill impairment		0
Currency translation adjustment	28,772	(7,882)
Goodwill, Gross, Ending Balance	368,637	339,865
Accumulated Impairment Loss, Ending Balance	0	0
Goodwill, Ending Balance	368,637	339,865
U.K./European Operations [Member]
Goodwill [Roll Forward]
Goodwill, Gross, Beginning Balance	167,276	182,029
Accumulated Impairment Loss, Beginning Balance	14,482
Goodwill, Beginning Balance	152,794
Goodwill acquired	11,849	0
Acquisition accounting adjustments	0	9,736
Goodwill impairment		(14,482)
Currency translation adjustment	15,157	(24,489)
Goodwill, Gross, Ending Balance	194,282	167,276
Accumulated Impairment Loss, Ending Balance	(14,482)	14,482
Goodwill, Ending Balance	$ 179,800	$ 152,794