Debt - Mortgages Payable (Details) - USD ($)	3 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Total Principal	$ 1,371,238,000
Total	1,370,999,000
Mortgages [Member]
Debt Instrument [Line Items]
Total Principal	33,238,000	$ 33,434,000
Unamortized debt issuance costs	(285,000)	(312,000)
Total	32,953,000	33,122,000
Notes Payable Due January 2023 3.60 Percent [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Total Principal	$ 23,640,000	23,640,000
Debt Instrument, Interest Rate, Stated Percentage	3.60%
Notes Payable Due September 2023 5.01 Percent [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Total Principal	$ 4,622,000	4,622,000
Debt Instrument, Interest Rate, Stated Percentage	5.01%
Notes Payable Due July 2026 6.27 Percent [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Total Principal	$ 4,976,000	$ 5,172,000
Debt Instrument, Periodic Payment, Principal	$ 91,675
Debt Instrument, Interest Rate, Stated Percentage	6.27%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
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-Name Accounting Standards Codification
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-Section S99
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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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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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Amount of the required periodic payments applied to principal.

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

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-Publisher FASB
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-Topic 210
-SubTopic 10
-Section S99
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
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