Schedule III Real Estate and Accumulated Depreciation (Parenthetical) (Details)	12 Months Ended
Dec. 31, 2017 USD ($) Contract
Real Estate and Accumulated Depreciation [Line Items]
SEC Schedule III, Real Estate, Federal Income Tax Basis	$ 10,800,000,000
Encumbrance 1 \| FNMA
Real Estate and Accumulated Depreciation [Line Items]
Secured credit facilities, amount available	80,000,000
Line of credit facility, amount outstanding	$ 80,000,000
Variable interest rate (percent)	1.80%
Encumbrance 1 \| FNMA \| Interest Rate Swap
Real Estate and Accumulated Depreciation [Line Items]
Number of Interest rate derivatives held (contracts) \| Contract	1
Variable rate borrowings after interest rate swaps (percent)	4.50%
Encumbrance 1 \| FNMA \| Interest Rate Cap
Real Estate and Accumulated Depreciation [Line Items]
Derivative, Notional Amount	$ 25,000,000
Encumbrance 2 \| Fixed Rate Debt \| Loan [Member]
Real Estate and Accumulated Depreciation [Line Items]
Amount of bond used as encumbrance	$ 125,200,000.0
Derivative cap interest rate (percent)	5.08%
Derivative termination date	Jun. 10, 2021
Furniture, fixtures and equipment
Real Estate and Accumulated Depreciation [Line Items]
Estimated useful lives (years)	5 years
Minimum \| Land improvements and buildings
Real Estate and Accumulated Depreciation [Line Items]
Estimated useful lives (years)	8 years
Maximum \| Land improvements and buildings
Real Estate and Accumulated Depreciation [Line Items]
Estimated useful lives (years)	40 years
Corporate Real Estate Owned \| Minimum
Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation, Life Used for Depreciation	1 year
Corporate Real Estate Owned \| Maximum
Real Estate and Accumulated Depreciation [Line Items]
Real Estate and Accumulated Depreciation, Life Used for Depreciation	40 years

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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Debt Instrument, Effective Interest Rate, Percentage after Interest Rate Swap

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Cap rate on an interest rate derivative such as an interest rate cap or collar. If market rates exceed the cap rate, a payment or receipt is triggered on the contract.

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Date the derivative contract matures, in CCYY-MM-DD format.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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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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The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

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Number of interest rate derivative instruments held by the entity at the reporting date.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Useful life on which depreciation was computed for entities with a substantial portion of business acquiring and holding investment real estate, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Cost basis of real estate investments for federal income tax purposes for entities with a substantial portion of business acquiring and holding investment real estate.

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