Long-Term Debt and Notes Payable - Components of Long-Term Debt And Notes Payable (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Principal Outstanding	$ 3,380,284	$ 2,744,080
Unamortized Premium (Discount)	(13,471)	(13,924)
Unamortized Issuance Costs	(37,105)	(30,254)
Carrying Value	3,329,708	2,699,902
Fair Value	3,403,537	2,761,735
Select Excluding Concentra
Debt Instrument [Line Items]
Principal Outstanding	1,956,754	2,118,252
Unamortized Premium (Discount)	(10,393)	(11,667)
Unamortized Issuance Costs	(16,688)	(19,586)
Carrying Value	1,929,673	2,086,999
Fair Value	$ 1,967,001	2,129,909
Select Excluding Concentra \| Senior notes \| 6.375% Senior Notes Due June 2021
Debt Instrument [Line Items]
Interest rate of debt (as a percent)	6.375%
Principal Outstanding	$ 710,000	710,000
Unamortized Premium (Discount)	607	778
Unamortized Issuance Costs	(5,122)	(6,553)
Carrying Value	705,485	704,225
Fair Value	718,875	727,750
Select Excluding Concentra \| Other
Debt Instrument [Line Items]
Principal Outstanding	49,004	36,877
Unamortized Premium (Discount)	0	0
Unamortized Issuance Costs	(508)	(533)
Carrying Value	48,496	36,344
Fair Value	48,496	36,344
Select Excluding Concentra \| Revolving facility \| Credit facilities
Debt Instrument [Line Items]
Principal Outstanding	65,000	230,000
Unamortized Premium (Discount)	0	0
Unamortized Issuance Costs	0	0
Carrying Value	65,000	230,000
Fair Value	59,800	211,600
Select Excluding Concentra \| Term loans \| Credit facilities
Debt Instrument [Line Items]
Principal Outstanding	1,132,750	1,141,375
Unamortized Premium (Discount)	(11,000)	(12,445)
Unamortized Issuance Costs	(11,058)	(12,500)
Carrying Value	1,110,692	1,116,430
Fair Value	1,139,830	1,154,215
Concentra Inc
Debt Instrument [Line Items]
Principal Outstanding	1,423,530	625,828
Unamortized Premium (Discount)	(3,078)	(2,257)
Unamortized Issuance Costs	(20,417)	(10,668)
Carrying Value	1,400,035	612,903
Fair Value	1,436,536	631,826
Concentra Inc \| Other
Debt Instrument [Line Items]
Principal Outstanding	9,355	6,653
Unamortized Premium (Discount)	0	0
Unamortized Issuance Costs	0	0
Carrying Value	9,355	6,653
Fair Value	9,355	6,653
Concentra Inc \| Term loans \| Credit facilities
Debt Instrument [Line Items]
Principal Outstanding	1,414,175	619,175
Unamortized Premium (Discount)	(3,078)	(2,257)
Unamortized Issuance Costs	(20,417)	(10,668)
Carrying Value	1,390,680	606,250
Fair Value	$ 1,427,181	$ 625,173

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Name Accounting Standards Codification
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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after accumulated amortization, of debt discount (premium).

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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