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Debt - Mortgages and Other Notes Payable - Additional Information (Details) $ in Thousands			3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 29, 2021	Oct. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) Mortgage	Jun. 30, 2021 USD ($)	Sep. 30, 2021 USD ($) Mortgage	Dec. 31, 2020 USD ($) Mortgage	Sep. 29, 2021	Mar. 31, 2021 USD ($)	Jul. 31, 2020 USD ($)	Feb. 29, 2020 USD ($)
Debt Instrument [Line Items]
Notes receivable, net			$ 101,450		$ 158,468	$ 101,450
Maximum borrowing capacity					900,000
Canton Marketplace
Debt Instrument [Line Items]
Mortgage					$ 31,800
Mortgages
Debt Instrument [Line Items]
Number of mortgage loans \| Mortgage					9
Number of properties collateralized \| Mortgage			42		38	42
Mortgages \| Canton Marketplace
Debt Instrument [Line Items]
Mortgage					$ 31,800
Interest rate, stated percentage					3.35%
Debt instrument, maturity date					May 01, 2023
Mortgages \| Subscription Line
Debt Instrument [Line Items]
Number of mortgage loans \| Mortgage						7
Notes receivable, net			$ 46,000			$ 46,000		$ 37,200
Note receivable principal amount								$ 1,700
Mortgages \| Subscription Line 1
Debt Instrument [Line Items]
Notes receivable, net			51,300			51,300
Mortgages \| Subscription Line 2
Debt Instrument [Line Items]
Notes receivable, net			40,000	$ 125,100		40,000
Note receivable principal amount				6,500	$ 10,200
Mortgages \| Subscription Line 3
Debt Instrument [Line Items]
Notes receivable, net			88,000		53,000	88,000
Fund IV
Debt Instrument [Line Items]
Repayments of debt					$ 23,500
Fund IV \| Bridge Facility
Debt Instrument [Line Items]
Maximum borrowing capacity				79,200
Repayments of debt				$ 10,000
Maturity date	Jun. 30, 2021			Dec. 31, 2021
LIBOR plus					2.50%		2.00%
LIBOR floor					0.25%
Fund IV \| Mortgages
Debt Instrument [Line Items]
Holdback mortgage loan			23,800			23,800
Holdback mortgage loan outstanding			18,900			18,900
Holdback mortgage loan drew an additional					$ 1,000				$ 900
Fund IV \| Mortgages One \| Colonie Plaza - Albany, NY
Debt Instrument [Line Items]
Repayments of debt						11,600
Core Portfolio
Debt Instrument [Line Items]
Repayments of debt						26,300
Derivative, notional amount					539,636
Core Portfolio \| Sixty Orange Street \| Disposed of by sale
Debt Instrument [Line Items]
Repayments of debt					6,700
Scheduled principal payment					6,300
Core Portfolio \| Mortgages \| Brandywine Portfolio
Debt Instrument [Line Items]
Debt default, amount					26,300
Debt instrument, maturity date				Jul. 01, 2016
Gain (loss) on litigation settlement		$ 30,000
Acquisition of noncontrolling interest		$ 15,900
Core Portfolio \| Mortgages \| Brandywine Portfolio \| Acadia's OP Ownership
Debt Instrument [Line Items]
Equity interest held by Operating Partnership		77.78%
Core Portfolio \| Mortgages \| Realized and Unrealized Holding Gains (Losses) on Investments and Other \| Brandywine Portfolio
Debt Instrument [Line Items]
Gain on debt extinguishment			18,300
Proportionate share		$ 4,100
Fund II \| Mortgages
Debt Instrument [Line Items]
Notes receivable, net			200,000			200,000
Fund III and Fund IV \| Mortgages
Debt Instrument [Line Items]
Holdback mortgage loan			103,400			103,400
Fund Loans Repaid			11,500			11,500
Interest Rate Swaps
Debt Instrument [Line Items]
Derivative, notional amount			$ 30,400			$ 30,400				$ 50,000
Interest Rate Swaps \| New Towne Plaza
Debt Instrument [Line Items]
Derivative, notional amount					16,700
Cash proceeds from swaps					$ 3,400