| **Business Combinations - Table 1 (Details) - USD ($) $ in Millions**                                           | Sep. 30, 2016 | Aug. 31, 2016 | Dec. 31, 2015 |
|-----------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|
| **Business Acquisition [Line Items]**                                                                           |          |          |          |
| Goodwill                                                                                                        | $ 1,915.6     |          | $ 1,890.1     |
| Hot Springs, Bryan and Broken Arrow [Member] | Noncompete Agreements [Member]                                   |          |          |          |
| **Business Acquisition [Line Items]**                                                                           |          |          |          |
| Identifiable intangible assets                                                                                  |          | $ 0.4         |          |
| Inpatient Rehabilitation Segment [Member] | Hot Springs, Bryan and Broken Arrow [Member]                        |          |          |          |
| **Business Acquisition [Line Items]**                                                                           |          |          |          |
| Property and equipment                                                                                          |          | 5.3           |          |
| Goodwill                                                                                                        |          | 9.4           |          |
| Total assets acquired                                                                                           |          | 16.1          |          |
| Inpatient Rehabilitation Segment [Member] | Hot Springs, Bryan and Broken Arrow [Member] | Trade Names [Member] |          |          |          |
| **Business Acquisition [Line Items]**                                                                           |          |          |          |
| Identifiable intangible assets                                                                                  |          | $ 1.0         |          |

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.
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