Income Taxes - Reconciliation of Effective Tax Rate (Details)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Taxes at statutory U.S. federal income tax rate	21.00%	35.00%	35.00%
Nontaxable income of SNH	(21.00%)	(35.00%)	(35.00%)
State and local income taxes, net of federal tax benefit	0.10%	0.30%	0.30%
TCJA Adjustment	0.00%	9.00%	0.00%
Change in valuation allowance	1.90%	(6.50%)	3.60%
Other differences, net	(1.90%)	(2.50%)	(3.60%)
Effective tax rate	0.10%	0.30%	0.30%

Effective Income Tax Rate Reconciliation, Tax Cuts And Jobs Act Of 2017, Percent

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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