Acquisitions - U.S. HealthWorks Acquisition (Details) - USD ($) $ in Thousands		3 Months Ended	8 Months Ended	9 Months Ended
	Feb. 01, 2018	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Acquisitions
Non-cash equity exchange for acquisition of U.S. HealthWorks		$ 238,000	$ 238,000	$ 238,000		$ 0
Consideration given for the acquired business
Goodwill		3,311,459	3,311,459	3,311,459	$ 2,782,812
U.S. HealthWorks
Acquisitions
U.S. HealthWorks acquisition costs				$ 2,900
Total consideration (net of cash acquired)	$ 753,000
Estimated value of goodwill, deductible for tax purposes	83,100
Net revenues of acquiree		$ 133,300	$ 362,700
Consideration given for the acquired business
Identifiable tangible assets	184,163
Identifiable intangible assets	140,406
Goodwill	533,124
Total assets	857,693
Total liabilities	104,693
Consideration given	753,000
U.S. HealthWorks | Customer relationships
Consideration given for the acquired business
Identifiable intangible assets	$ 135,000
Identifiable intangible assets
Weighted Average Amortization Period	15 years
U.S. HealthWorks | Trademarks
Consideration given for the acquired business
Identifiable intangible assets	$ 5,000
Identifiable intangible assets
Weighted Average Amortization Period	1 year
U.S. HealthWorks | Favorable leasehold interests
Consideration given for the acquired business
Identifiable intangible assets	$ 406
Identifiable intangible assets
Weighted Average Amortization Period	2 years 10 months 24 days
Concentra Group Holdings Parent, LLC | U.S. HealthWorks
Acquisitions
Equity interest issued (percent)	20.00%
Non-cash equity exchange for acquisition of U.S. HealthWorks	$ 238,000