Mortgages Payable - Summary of Maturities (Details) - Mortgages payable - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Maturity of mortgages payable
2021	$ 900
2022	111,600
2023	20,400
2024	111,900
2025	40,800
Net payable amount	$ 285,617	$ 300,360

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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