Fair Value Measurements - Available for Sale (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Recurring \| Level 2 \| Interest rate swap
Financial assets:
Derivative financial instruments	$ 4,793,000	$ 1,615,000
Financial liabilities:
Derivative financial instruments		1,492,000
Facility
Fair Value of Financial Instruments
Line of credit, gross	0	9,400,000
Mortgages payable
Fair Value of Financial Instruments
Estimated fair value of mortgages payable	392,836,000	397,103,000
Carrying value of mortgage loans	407,007,000	396,946,000
Excess of carrying value over fair value	$ 14,171,000
Excess of fair value over carrying value		$ 157,000
Weighted average remaining term of the mortgages	8 years 6 months	8 years 8 months 12 days
Blended market interest rate \| Mortgages payable
Fair Value of Financial Instruments
Mortgages payable	4.90%	4.25%

Represents the amount of difference between the carrying value and the fair value.

No definition available.

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- Definition

Represents the amount of difference between the fair value and carrying value.

+ References

No definition available.

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- Definition

Represents the weighted average remaining term of the mortgages based on which the market interest rate is assumed.

+ References

No definition available.

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- Definition

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 before netting of deferred finance costs, 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) post balance 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 cancellable 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.

+ References

No definition available.

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- Definition

Value of input used to measure mortgages payable.

+ References

No definition available.

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- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations before netting of deferred finance costs (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

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- References

No definition available.

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
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- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

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- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

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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.

+ References

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