Basis of Presentation - Table 1 (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($) state	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) state	Sep. 30, 2017 USD ($)	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Net operating revenues	$ 1,067.6	$ 981.6	$ 3,181.3	$ 2,905.1
Number of states in which entity operates | state	36		36
Inpatient Rehabilitation Segment [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	$ 825.6	783.5	$ 2,500.5	2,338.9
Number of states in which entity operates | state	31		31
Home Health and Hospice Segment [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	$ 242.0	198.1	$ 680.8	566.2
Number of states in which entity operates | state	30		30
Net operating revenues [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	$ 1,067.6	981.6	$ 3,181.3	2,905.1
Net operating revenues [Member] | Other income [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	15.6	11.3	37.3	31.2
Net operating revenues [Member] | Inpatient Rehabilitation Segment [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	825.6	783.5	2,500.5	2,338.9
Net operating revenues [Member] | Inpatient Rehabilitation Segment [Member] | Other income [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	15.3	11.1	36.6	30.6
Net operating revenues [Member] | Home Health and Hospice Segment [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	242.0	198.1	680.8	566.2
Net operating revenues [Member] | Home Health and Hospice Segment [Member] | Other income [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	0.3	0.2	0.7	0.6
Net operating revenues [Member] | Third-Party Payor [Member] | Medicare [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	806.2	746.2	2,413.9	2,202.9
Net operating revenues [Member] | Third-Party Payor [Member] | Medicare Advantage [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	97.7	82.6	290.7	251.8
Net operating revenues [Member] | Third-Party Payor [Member] | Managed Care [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	93.7	90.6	281.6	274.5
Net operating revenues [Member] | Third-Party Payor [Member] | Medicaid [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	29.8	26.4	84.5	73.5
Net operating revenues [Member] | Third-Party Payor [Member] | Other third-party payors [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	11.8	12.5	36.5	36.4
Net operating revenues [Member] | Third-Party Payor [Member] | Workers' compensation [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	7.4	7.2	21.9	21.2
Net operating revenues [Member] | Third-Party Payor [Member] | Inpatient Rehabilitation Segment [Member] | Medicare [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	600.5	576.3	1,832.1	1,719.2
Net operating revenues [Member] | Third-Party Payor [Member] | Inpatient Rehabilitation Segment [Member] | Medicare Advantage [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	75.0	63.5	226.2	195.4
Net operating revenues [Member] | Third-Party Payor [Member] | Inpatient Rehabilitation Segment [Member] | Managed Care [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	85.1	82.8	256.7	253.0
Net operating revenues [Member] | Third-Party Payor [Member] | Inpatient Rehabilitation Segment [Member] | Medicaid [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	25.7	25.5	77.2	70.2
Net operating revenues [Member] | Third-Party Payor [Member] | Inpatient Rehabilitation Segment [Member] | Other third-party payors [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	11.8	12.5	36.5	36.4
Net operating revenues [Member] | Third-Party Payor [Member] | Inpatient Rehabilitation Segment [Member] | Workers' compensation [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	6.9	7.2	21.1	21.1
Net operating revenues [Member] | Third-Party Payor [Member] | Home Health and Hospice Segment [Member] | Medicare [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	205.7	169.9	581.8	483.7
Net operating revenues [Member] | Third-Party Payor [Member] | Home Health and Hospice Segment [Member] | Medicare Advantage [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	22.7	19.1	64.5	56.4
Net operating revenues [Member] | Third-Party Payor [Member] | Home Health and Hospice Segment [Member] | Managed Care [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	8.6	7.8	24.9	21.5
Net operating revenues [Member] | Third-Party Payor [Member] | Home Health and Hospice Segment [Member] | Medicaid [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	4.1	0.9	7.3	3.3
Net operating revenues [Member] | Third-Party Payor [Member] | Home Health and Hospice Segment [Member] | Other third-party payors [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	0.0	0.0	0.0	0.0
Net operating revenues [Member] | Third-Party Payor [Member] | Home Health and Hospice Segment [Member] | Workers' compensation [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	0.5	0.0	0.8	0.1
Net operating revenues [Member] | Self-Pay [Member] | Patients [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	5.4	4.8	14.9	13.6
Net operating revenues [Member] | Self-Pay [Member] | Inpatient Rehabilitation Segment [Member] | Patients [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	5.3	4.6	14.1	13.0
Net operating revenues [Member] | Self-Pay [Member] | Home Health and Hospice Segment [Member] | Patients [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues	$ 0.1	$ 0.2	$ 0.8	$ 0.6
Accounts receivable [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues by payor source (percent)			100.00%		100.00%
Accounts receivable [Member] | Third-Party Payor [Member] | Medicare [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues by payor source (percent)			74.50%		75.10%
Accounts receivable [Member] | Third-Party Payor [Member] | Managed Care, Medicare Advantage and Other Discount Plans [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues by payor source (percent)			17.80%		17.40%
Accounts receivable [Member] | Third-Party Payor [Member] | Medicaid [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues by payor source (percent)			2.80%		2.40%
Accounts receivable [Member] | Third-Party Payor [Member] | Other third-party payors [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues by payor source (percent)			2.80%		2.90%
Accounts receivable [Member] | Third-Party Payor [Member] | Workers' compensation [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues by payor source (percent)			1.20%		1.30%
Accounts receivable [Member] | Self-Pay [Member] | Patients [Member] | Payor Source [Member]
Disaggregation of Revenue [Line Items]
Net operating revenues by payor source (percent)			0.90%		0.90%