Notes Payable and Unsecured Credit Facilities Schedule of maturities of long-term debt (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
2021	$ 30,558
2022	17,237
2023	74,571
2024	345,591
2025	293,732
Beyond 5 Years	3,011,817
Unamortized debt premium/(discount) and issuance costs	(24,233)
Total	3,749,273	$ 3,923,084
Unsecured Debt [Member]
Debt Instrument [Line Items]
Total	3,242,896	$ 3,239,609
Scheduled Principal Payments [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
2021	2,808
2022	11,389
2023	9,695
2024	4,849
2025	3,732
Beyond 5 Years	10,583
Unamortized debt premium/(discount) and issuance costs	0
Total	43,056
Mortgage Loan Maturities \| Mortgages [Member]
Debt Instrument [Line Items]
2021	27,750
2022	5,848
2023	64,876
2024	90,742
2025	40,000
Beyond 5 Years	226,234
Unamortized debt premium/(discount) and issuance costs	7,871
Total	463,321
Unsecured Maturities [Member] \| Unsecured Debt [Member]
Debt Instrument [Line Items]
2021	0
2022	0
2023	0
2024	250,000
2025	250,000
Beyond 5 Years	2,775,000
Unamortized debt premium/(discount) and issuance costs	(32,104)
Total	$ 3,242,896

Long term debt maturities repayments of principal thereafter.

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