Long-Term Debt and Notes Payable - 2017 Select Credit Facilities (Details)		12 Months Ended
	Mar. 06, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Long-term debt and notes payable
Total principal		$ 2,744,080,000	$ 2,747,856,000
Select Excluding Concentra
Long-term debt and notes payable
Total principal		2,118,252,000	2,100,439,000
Select Excluding Concentra | Term loan | Credit facility
Long-term debt and notes payable
Total principal		1,141,375,000	1,147,751,000
Select Excluding Concentra | Revolving facility | Credit facility
Long-term debt and notes payable
Total principal		$ 230,000,000	$ 220,000,000
Select Excluding Concentra | 2017 Select Credit Facilities | Credit facility
Long-term debt and notes payable
Current borrowing capacity	$ 1,600,000,000
Percentage of net cash proceeds received from non-ordinary course asset sales or other dispositions, or as a result of a casualty or condemnation to be used for prepayment of debt	100.00%
Percentage of net proceeds received from the issuance of debt obligations other than certain permitted debt obligations to be used for prepayment of debt	100.00%
Percentage of capital stock of foreign subsidiaries		65.00%
Select Excluding Concentra | 2017 Select Credit Facilities | Credit facility | Leverage ratio greater than 4.50 to 1.00
Long-term debt and notes payable
Percentage of excess cash flow to be used for prepayment of debt	50.00%
Leverage ratio of financial maintenance covenant	4.50
Select Excluding Concentra | 2017 Select Credit Facilities | Credit facility | Leverage ratio less than or equal to 4.50 to 1.00 and greater than 4.00 to 1.00
Long-term debt and notes payable
Percentage of excess cash flow to be used for prepayment of debt	25.00%
Select Excluding Concentra | 2017 Select Credit Facilities | Credit facility | Leverage ratio less than or equal to 4.50 to 1.00 and greater than 4.00 to 1.00 | Maximum
Long-term debt and notes payable
Leverage ratio of financial maintenance covenant	4.50
Select Excluding Concentra | 2017 Select Credit Facilities | Credit facility | Leverage ratio less than or equal to 4.50 to 1.00 and greater than 4.00 to 1.00 | Minimum
Long-term debt and notes payable
Leverage ratio of financial maintenance covenant	4.00
Select Excluding Concentra | 2017 Select Credit Facilities | Credit facility | Leverage ratio less than 4.00 to 1.00
Long-term debt and notes payable
Leverage ratio of financial maintenance covenant	4.00
Select Excluding Concentra | 2017 Select Credit Facilities | Term loan | Credit facility
Long-term debt and notes payable
Aggregate principal amount	$ 1,150,000,000.00
Debt instrument term (in years)	7 years
Amortization of term loan	0.25%
Total principal		$ 1,141,400,000
Unamortized discounts and debt issuance costs		$ 24,900,000
Select Excluding Concentra | 2017 Select Credit Facilities | Term loan | Credit facility | Adjusted LIBO
Long-term debt and notes payable
Interest rate margin (as a percent)	3.50%
Select Excluding Concentra | 2017 Select Credit Facilities | Term loan | Credit facility | Adjusted LIBO Rate floor
Long-term debt and notes payable
Interest rate margin (as a percent)	1.00%
Select Excluding Concentra | 2017 Select Credit Facilities | Term loan | Credit facility | Alternate Base Rate
Long-term debt and notes payable
Interest rate margin (as a percent)	2.50%
Select Excluding Concentra | 2017 Select Credit Facilities | Term loan | Credit facility | Alternate Base Rate floor
Long-term debt and notes payable
Interest rate margin (as a percent)	2.00%
Select Excluding Concentra | 2017 Select Credit Facilities | Revolving facility | Credit facility
Long-term debt and notes payable
Current borrowing capacity	$ 450,000,000
Debt instrument term (in years)	5 years
Leverage ratio of financial maintenance covenant		5.27
Commitment fee (as a percent)		0.50%
Total principal		$ 230,000,000
Remaining borrowing capacity		$ 181,400,000
Select Excluding Concentra | 2017 Select Credit Facilities | Revolving facility | Credit facility | Leverage ratio less than 6.25 to 1.00 | Maximum
Long-term debt and notes payable
Leverage ratio of financial maintenance covenant	6.25
Select Excluding Concentra | 2017 Select Credit Facilities | Revolving facility | Credit facility | Future leverage ratio required less than 6.00 to 1.00 | Maximum
Long-term debt and notes payable
Leverage ratio of financial maintenance covenant	6.00
Select Excluding Concentra | 2017 Select Credit Facilities | Revolving facility | Credit facility | Adjusted LIBO
Long-term debt and notes payable
Interest rate margin (as a percent)		3.25%
Select Excluding Concentra | 2017 Select Credit Facilities | Revolving facility | Credit facility | Adjusted LIBO | Maximum
Long-term debt and notes payable
Interest rate margin (as a percent)	3.25%
Select Excluding Concentra | 2017 Select Credit Facilities | Revolving facility | Credit facility | Adjusted LIBO | Minimum
Long-term debt and notes payable
Interest rate margin (as a percent)	3.00%
Select Excluding Concentra | 2017 Select Credit Facilities | Revolving facility | Credit facility | Alternate Base Rate
Long-term debt and notes payable
Interest rate margin (as a percent)		2.25%
Select Excluding Concentra | 2017 Select Credit Facilities | Revolving facility | Credit facility | Alternate Base Rate | Maximum
Long-term debt and notes payable
Interest rate margin (as a percent)	2.25%
Select Excluding Concentra | 2017 Select Credit Facilities | Revolving facility | Credit facility | Alternate Base Rate | Minimum
Long-term debt and notes payable
Interest rate margin (as a percent)	2.00%
Select Excluding Concentra | 2017 Select Credit Facilities | Letter of credit | Credit facility
Long-term debt and notes payable
Current borrowing capacity	$ 75,000,000
Outstanding letters of credit		$ 38,600,000