Investments in Real Estate Partnerships - Scheduled Principal Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
2020	$ 50,359
2021	85,699
2022	802,645
2023	69,498
2024	346,043
Beyond 5 Years	2,592,015
Unamortized debt discounts (premiums)	(26,715)
Long-term Debt	3,919,544	$ 3,715,212
Unsecured Debt [Member]
Schedule of Equity Method Investments [Line Items]
Long-term Debt	2,944,752	$ 2,475,322
Unconsolidated Investments in Partnership [Member]
Schedule of Equity Method Investments [Line Items]
2020	355,651
2021	300,625
2022	178,513
2023	174,597
2024	35,203
Beyond 5 Years	540,788
Unamortized debt discounts (premiums)	(7,910)
Long-term Debt	1,577,467
Unconsolidated Investments in Partnership [Member] \| Mortgages [Member] \| Scheduled Principal Payments [Member]
Schedule of Equity Method Investments [Line Items]
2020	17,043
2021	11,048
2022	7,811
2023	2,989
2024	1,513
Beyond 5 Years	6,555
Unamortized debt discounts (premiums)	0
Long-term Debt	46,959
Unconsolidated Investments in Partnership [Member] \| Mortgages [Member] \| Mortgage Loan Maturities [Member]
Schedule of Equity Method Investments [Line Items]
2020	338,608
2021	269,942
2022	170,702
2023	171,608
2024	33,690
Beyond 5 Years	534,233
Unamortized debt discounts (premiums)	(7,910)
Long-term Debt	1,510,873
Unconsolidated Investments in Partnership [Member] \| Unsecured Debt [Member] \| Unsecured Maturities [Member]
Schedule of Equity Method Investments [Line Items]
2020	0
2021	19,635
2022	0
2023	0
2024	0
Beyond 5 Years	0
Unamortized debt discounts (premiums)	0
Long-term Debt	19,635
Unconsolidated Investments in Partnership, Pro-rata Share [Member] [Member]
Schedule of Equity Method Investments [Line Items]
2020	115,953
2021	104,375
2022	68,417
2023	65,096
2024	14,160
Beyond 5 Years	160,472
Unamortized debt discounts (premiums)	(2,425)
Long-term Debt	$ 526,048

Amount, after accumulated amortization, of debt discount (premium).

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