Debt - Mortgage Payable - Additional Information (Details)				1 Months Ended	3 Months Ended	9 Months Ended		12 Months Ended
	Oct. 02, 2020	Jun. 24, 2020 USD ($)	Nov. 09, 2017 USD ($)	Oct. 31, 2020	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) property loan	Sep. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($) property loan	Dec. 31, 2012 USD ($)	Jul. 31, 2020 USD ($)
Debt Instrument [Line Items]
Notes receivable, net						$ 134,798,000			$ 114,943,000
Fund mortgages aggregate outstanding balances						134,798,000			114,943,000
Fund loans aggregating						1,800,000
Fund loans repaid						700,000
Scheduled principal payment						4,200,000
Mortgages
Debt Instrument [Line Items]
Fund mortgages aggregate outstanding, that had not met debt yield						$ 177,700,000
Scheduled principal payment									5,900,000
Borrowings, amount									$ 258,900,000
Number of properties collateralized | property						43			44
Mortgages | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate									1.70%
Mortgages | Acadia Realty Trust
Debt Instrument [Line Items]
Fund mortgages aggregate outstanding, that had not met debt yield						$ 36,200,000
Mortgages | Subscription Line
Debt Instrument [Line Items]
Notes receivable, net						55,400,000
Fund mortgages aggregate outstanding balances						55,400,000
Mortgages | Maturing from May 2019 to January 2021
Debt Instrument [Line Items]
Number of mortgage loans | loan									3
Borrowings, amount									$ 69,000,000.0
Mortgages | Maturing from May 2019 to January 2021 | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate									2.08%
Mortgages | Maturing from April 2022 though December 2024.
Debt Instrument [Line Items]
Borrowings, amount									$ 71,800,000
Mortgages | Maturing from April 2022 though December 2024. | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate									1.86%
Mortgages | Maturities Ranging from November 2019 through January 2020
Debt Instrument [Line Items]
Number of mortgage loans | loan									3
Borrowings, amount									$ 135,900,000
Mortgages | Maturities Ranging from November 2019 through January 2020 | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate									3.65%
Mortgages | Maturing Ranging from December 2020 though May 2021
Debt Instrument [Line Items]
Borrowings, amount									$ 125,300,000
Mortgages | Maturing Ranging from December 2020 though May 2021 | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate									2.96%
Mortgages | Interest Rate Swaps
Debt Instrument [Line Items]
Derivative, notional amount									$ 283,600,000
Derivative weighted average interest rate									1.78%
Fund II | New Market Tax Credit
Debt Instrument [Line Items]
Percentage of tax credits on qualifying invested equity loans					39.00%
Transfer of tax credit transactions to investors exchange amount										$ 5,200,000
Redemption of loan expiration period							7 years
Fund II | New Market Tax Credit | Other Income
Debt Instrument [Line Items]
Income recognized from tax credit transactions					$ 5,000,000.0		$ 5,000,000.0		$ 1,400,000
Fund II | City Point Project | New Market Tax Credit
Debt Instrument [Line Items]
Income recognized from tax credit transactions					$ 5,000,000.0
Fund II | Mortgages
Debt Instrument [Line Items]
Notes receivable, net						200,000,000.0
Number of mortgage loans | loan									1
Fund mortgages aggregate outstanding balances						200,000,000.0
Fund V | Mortgages
Debt Instrument [Line Items]
Notes receivable, net						150,000,000.0
Number of mortgage loans | loan									5
Fund mortgages aggregate outstanding balances						150,000,000.0
Fund V | Mortgages | Subscription Line
Debt Instrument [Line Items]
Notes receivable, net						$ 75,400,000
Number of mortgage loans | loan						5
Fund mortgages aggregate outstanding balances						$ 75,400,000
Fund IV | Mortgages
Debt Instrument [Line Items]
Number of mortgage loans | loan									3
Holdback mortgage loan						23,800,000
Holdback mortgage loan outstanding						18,900,000
Holdback mortgage loan drew an additional						1,000,000.0					$ 900,000
Repayments of debt									$ 38,200,000
Fund IV | Mortgages | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate									2.35%
Fund IV | Mortgages One | Colonie Plaza
Debt Instrument [Line Items]
Repayments of debt						11,600,000
Fund IV | Mortgages Two
Debt Instrument [Line Items]
Repayments of debt									$ 18,400,000
Fund III | Mortgages
Debt Instrument [Line Items]
Repayments of debt									$ 4,700,000
Fund III | Mortgages | LIBOR
Debt Instrument [Line Items]
Basis spread on variable rate									0.50%
Fund III | Mortgages One
Debt Instrument [Line Items]
Repayments of debt									$ 9,800,000
Core Portfolio
Debt Instrument [Line Items]
Derivative, notional amount						572,476,000
Core Portfolio | Mortgages | Brandywine Portfolio
Debt Instrument [Line Items]
Debt default, amount						$ 26,300,000			$ 26,300,000
Debt instrument, maturity date						Jul. 01, 2016
Interest rate, stated percentage						6.00%
Debt default interest						5.00%
Claim amount exclusive of accruing interest, default interest, late charges, and fees and costs			$ 33,000,000.0
Increase the alleged balance		$ 46,800,000
Default interest		300,000
Attorneys fees		200,000
Suspense funds		1,500,000						$ 1,300,000
Parties jointly and severally liable amount		33,200,000
Default interest per diem		$ 8,017
Legal and other costs								6,800,000
Proportionate share								$ 1,500,000
Core Portfolio | Mortgages | Brandywine Portfolio | Subsequent Event
Debt Instrument [Line Items]
Cross appeal stay period	90 days
Litigation settlement date				Oct. 30, 2020
Interest Rate Swaps
Debt Instrument [Line Items]
Derivative, notional amount						$ 50,000,000.0					$ 30,400,000