Investments in Real Estate Partnerships - Scheduled Principal Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
2017	$ 22,734
2018	389,867
2019	338,659
2020	727,646
2021	69,418
Beyond 5 Years	2,186,858
Unamortized debt discounts (premiums)	(19,970)
Long-term Debt	3,715,212	$ 3,594,977
Mortgages [Member]
Schedule of Equity Method Investments [Line Items]
Long-term Debt	403,306	520,193
Mortgages [Member] \| Scheduled Principal Payments [Member]
Schedule of Equity Method Investments [Line Items]
2017	9,518
2018	11,287
2019	11,599
2020	11,798
2021	10,043
Beyond 5 Years	27,013
Unamortized debt discounts (premiums)	0
Long-term Debt	81,258
Mortgages [Member] \| Mortgage Loan Maturities [Member]
Schedule of Equity Method Investments [Line Items]
2017	13,216
2018	78,580
2019	77,060
2020	5,848
2021	59,375
Beyond 5 Years	209,845
Unamortized debt discounts (premiums)	5,974
Long-term Debt	449,898
Unsecured Debt [Member]
Schedule of Equity Method Investments [Line Items]
Long-term Debt	2,475,322	$ 2,325,656
Unsecured Debt [Member] \| Unsecured Maturities [Member]
Schedule of Equity Method Investments [Line Items]
2017	0
2018	300,000
2019	250,000
2020	710,000
2021	0
Beyond 5 Years	1,950,000
Unamortized debt discounts (premiums)	(25,944)
Long-term Debt	3,184,056
Unconsolidated Investments in Partnership [Member]
Schedule of Equity Method Investments [Line Items]
2017	86,001
2018	343,626
2019	300,625
2020	178,513
2021	174,597
Beyond 5 Years	536,990
Unamortized debt discounts (premiums)	(10,705)
Long-term Debt	1,609,647
Unconsolidated Investments in Partnership [Member] \| Mortgages [Member] \| Scheduled Principal Payments [Member]
Schedule of Equity Method Investments [Line Items]
2017	20,062
2018	17,043
2019	11,048
2020	7,811
2021	2,989
Beyond 5 Years	7,353
Unamortized debt discounts (premiums)	0
Long-term Debt	66,306
Unconsolidated Investments in Partnership [Member] \| Mortgages [Member] \| Mortgage Loan Maturities [Member]
Schedule of Equity Method Investments [Line Items]
2017	65,939
2018	326,583
2019	269,942
2020	170,702
2021	171,608
Beyond 5 Years	529,637
Unamortized debt discounts (premiums)	(10,705)
Long-term Debt	1,523,706
Unconsolidated Investments in Partnership [Member] \| Unsecured Debt [Member] \| Unsecured Maturities [Member]
Schedule of Equity Method Investments [Line Items]
2017	0
2018	0
2019	19,635
2020	0
2021	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]
2017	22,294
2018	101,841
2019	104,375
2020	68,417
2021	65,096
Beyond 5 Years	175,032
Unamortized debt discounts (premiums)	(3,082)
Long-term Debt	$ 533,973

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

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