Acquisitions - Physiotherapy Acquisition (Details) - USD ($) $ in Thousands		12 Months Ended
	Mar. 04, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Consideration given for identifiable net assets and goodwill acquired to the net cash paid
Goodwill		$ 2,782,812	$ 2,751,000	$ 2,314,624
Net cash paid		$ 27,390	472,206	$ 1,061,628
Physiotherapy
Acquisitions
Voting equity interests acquired	100.00%
Acquisition costs			$ 3,200
Consideration given for identifiable net assets and goodwill acquired to the net cash paid
Cash and cash equivalents	$ 12,340
Identifiable tangible assets, excluding cash and cash equivalents	87,832
Identifiable intangible assets	32,484
Goodwill	343,187
Total assets	475,843
Total liabilities	54,685
Acquired non-controlling interests	2,514
Net assets acquired	418,644
Net cash paid	406,304
Estimated value of goodwill, deductible for tax purposes	$ 8,800