Commitments and Contingencies - Litigation (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) case_manager
Amended complaint | SSH-Evansville
Commitments and Contingencies
Number of case managers identified as plaintiff | case_manager	2
Professional liability claims
Commitments and Contingencies
Total annual aggregate limit of insurance coverage	$ 35.0
Joint Venture Operations [Member] | Minimum | Professional liability claims
Commitments and Contingencies
Total annual aggregate limit of insurance coverage	5.0
Joint Venture Operations [Member] | Maximum | Professional liability claims
Commitments and Contingencies
Total annual aggregate limit of insurance coverage	$ 20.0