Subsequent Events - Amendment to the Select Credit Facilities (Details) - Select Excluding Concentra - Credit facilities	Oct. 26, 2018	Mar. 22, 2018
2017 Select Credit Facilities Amendment | Adjusted LIBO | Term loans | Minimum
Debt Instrument [Line Items]
Interest rate margin (as a percent)		2.50%
2017 Select Credit Facilities Amendment | Adjusted LIBO | Term loans | Maximum
Debt Instrument [Line Items]
Interest rate margin (as a percent)		2.75%
2017 Select Credit Facilities Amendment | Adjusted LIBO | Revolving facility | Minimum
Debt Instrument [Line Items]
Interest rate margin (as a percent)		2.50%
2017 Select Credit Facilities Amendment | Adjusted LIBO | Revolving facility | Maximum
Debt Instrument [Line Items]
Interest rate margin (as a percent)		2.75%
2017 Select Credit Facilities Amendment | Alternate Base Rate | Term loans | Minimum
Debt Instrument [Line Items]
Interest rate margin (as a percent)		1.50%
2017 Select Credit Facilities Amendment | Alternate Base Rate | Term loans | Maximum
Debt Instrument [Line Items]
Interest rate margin (as a percent)		1.75%
2017 Select Credit Facilities Amendment | Alternate Base Rate | Revolving facility | Minimum
Debt Instrument [Line Items]
Interest rate margin (as a percent)		1.50%
2017 Select Credit Facilities Amendment | Alternate Base Rate | Revolving facility | Maximum
Debt Instrument [Line Items]
Interest rate margin (as a percent)		1.75%
Subsequent Event | Amendment No. 2, Select Credit Facilities | Adjusted LIBO | Term loans | Minimum
Debt Instrument [Line Items]
Interest rate margin (as a percent)	2.25%
Subsequent Event | Amendment No. 2, Select Credit Facilities | Adjusted LIBO | Term loans | Maximum
Debt Instrument [Line Items]
Interest rate margin (as a percent)	2.50%
Subsequent Event | Amendment No. 2, Select Credit Facilities | Adjusted LIBO | Revolving facility | Minimum
Debt Instrument [Line Items]
Interest rate margin (as a percent)	2.25%
Subsequent Event | Amendment No. 2, Select Credit Facilities | Adjusted LIBO | Revolving facility | Maximum
Debt Instrument [Line Items]
Interest rate margin (as a percent)	2.50%
Subsequent Event | Amendment No. 2, Select Credit Facilities | Alternate Base Rate | Term loans | Minimum
Debt Instrument [Line Items]
Interest rate margin (as a percent)	1.25%
Subsequent Event | Amendment No. 2, Select Credit Facilities | Alternate Base Rate | Term loans | Maximum
Debt Instrument [Line Items]
Interest rate margin (as a percent)	1.50%
Subsequent Event | Amendment No. 2, Select Credit Facilities | Alternate Base Rate | Revolving facility | Minimum
Debt Instrument [Line Items]
Interest rate margin (as a percent)	1.25%
Subsequent Event | Amendment No. 2, Select Credit Facilities | Alternate Base Rate | Revolving facility | Maximum
Debt Instrument [Line Items]
Interest rate margin (as a percent)	1.50%