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Debt - Mortgages and Other Notes Payable - Additional Information (Details) $ in Thousands			1 Months Ended	3 Months Ended		12 Months Ended
	Mar. 30, 2021	Oct. 30, 2020 USD ($)	Jan. 31, 2021 USD ($)	Mar. 31, 2021 USD ($) property loan	Dec. 31, 2020 USD ($) property	Dec. 31, 2020 USD ($) property loan	Jul. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Notes receivable, net				$ 101,410	$ 101,450	$ 101,450
Scheduled principal payment						$ 6,100
Amount of share failed to meet liquidity requirements				$ 8,700
Mortgages
Debt Instrument [Line Items]
Number of mortgage loans \| loan				3
Number of properties collateralized \| property				41	42	42
Mortgages \| Subscription Line
Debt Instrument [Line Items]
Number of mortgage loans \| loan						7
Notes receivable, net				$ 37,700	$ 46,000	$ 46,000
Mortgages \| Subscription Line 1
Debt Instrument [Line Items]
Notes receivable, net				23,100	51,300	51,300
Mortgages \| Subscription Line 2
Debt Instrument [Line Items]
Notes receivable, net					40,000	40,000
Mortgages \| Subscription Line 3
Debt Instrument [Line Items]
Notes receivable, net					88,000	88,000
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	2.00%			2.50%
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	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				$ 565,158
Core Portfolio \| Sixty Orange Street \| Disposed of by sale
Debt Instrument [Line Items]
Repayments of debt				6,700
Scheduled principal payment				$ 2,000
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 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
Fund III \| Mortgages
Debt Instrument [Line Items]
Term loans failed to meet liquidity requirements				$ 35,600
Interest Rate Swaps
Debt Instrument [Line Items]
Derivative, notional amount					$ 50,000	$ 50,000	$ 30,400
Interest Rate Swaps \| New Towne Plaza
Debt Instrument [Line Items]
Derivative, notional amount			$ 16,700
Cash proceeds from swaps			$ 3,400