Financial Instruments and Fair Value Measurements - Schedule of Items Measured at Fair Value on Nonrecurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Derivatives, Fair Value [Line Items]
Impairment charges	$ 9,925	$ 0		$ 9,925	$ 51,549
Fair Value, Measurements, Nonrecurring
Derivatives, Fair Value [Line Items]
Impairment charges				9,925		$ 85,598
Fair Value, Measurements, Nonrecurring | Acadia Realty Trust
Derivatives, Fair Value [Line Items]
Impairment charges				$ 2,294		$ 20,594
Cortlandt Crossing, Mohegan Lake, NY | Fair Value, Measurements, Nonrecurring | Fund III | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Triggering Event			Reduced holding period, reduced projected operating income
Impairment charges			$ 27,402
Cortlandt Crossing, Mohegan Lake, NY | Fair Value, Measurements, Nonrecurring | Fund III | Acadia Realty Trust | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Impairment charges			$ 6,726
654 Broadway, New York, NY | Fair Value, Measurements, Nonrecurring | Fund III | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Triggering Event			Reduced holding period
Impairment charges			$ 6,398
654 Broadway, New York, NY | Fair Value, Measurements, Nonrecurring | Fund III | Acadia Realty Trust | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Impairment charges			$ 1,570
146 Geary Street, San Francisco, CA | Fair Value, Measurements, Nonrecurring | Fund IV | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Triggering Event			Reduced holding period, reduced projected operating income
Impairment charges			$ 6,718
146 Geary Street, San Francisco, CA | Fair Value, Measurements, Nonrecurring | Fund IV | Acadia Realty Trust | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Impairment charges			$ 1,553
801 Madison Avenue, New York, NY | Fair Value, Measurements, Nonrecurring | Fund IV | Level 3 Inputs Fair Value of Net Assets Projections
Derivatives, Fair Value [Line Items]
Triggering Event			Reduced holding period, reduced projected operating income
Impairment charges			$ 11,031
801 Madison Avenue, New York, NY | Fair Value, Measurements, Nonrecurring | Fund IV | Acadia Realty Trust | Level 3 Inputs Fair Value of Net Assets Projections
Derivatives, Fair Value [Line Items]
Impairment charges			$ 2,551
717 N. Michigan Avenue, Chicago, IL | Fair Value, Measurements, Nonrecurring | Fund IV | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Triggering Event						Reduced holding period, reduced projected operating income
Impairment charges						$ 17,392
717 N. Michigan Avenue, Chicago, IL | Fair Value, Measurements, Nonrecurring | Fund IV | Acadia Realty Trust | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Impairment charges						$ 4,021
110 University, New York, NY | Fair Value, Measurements, Nonrecurring | Fund IV | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Triggering Event						Reduced holding period, reduced projected operating income
Impairment charges						$ 16,238
110 University, New York, NY | Fair Value, Measurements, Nonrecurring | Fund IV | Acadia Realty Trust | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Impairment charges						$ 3,754
Fifth Wall Investment | Fair Value, Measurements, Nonrecurring | Core Portfolio | Level 3 Inputs Fair Value of Net Assets Projections
Derivatives, Fair Value [Line Items]
Triggering Event						Decline in fair value
Impairment charges						$ 419
Fifth Wall Investment | Fair Value, Measurements, Nonrecurring | Core Portfolio | Acadia Realty Trust | Level 3 Inputs Fair Value of Net Assets Projections
Derivatives, Fair Value [Line Items]
Impairment charges						$ 419
210 Bowery, Manhattan, NY | Fair Value, Measurements, Nonrecurring | Fund IV | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Triggering Event				Reduced projected operating income
Impairment charges				$ 3,016
210 Bowery, Manhattan, NY | Fair Value, Measurements, Nonrecurring | Fund IV | Acadia Realty Trust | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Impairment charges				$ 697
27 E. 61st Street Manhattan, NY | Fair Value, Measurements, Nonrecurring | Fund IV | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Triggering Event				Reduced projected operating income
Impairment charges				$ 6,909
27 E. 61st Street Manhattan, NY | Fair Value, Measurements, Nonrecurring | Fund IV | Acadia Realty Trust | Level 3 Inputs Projections
Derivatives, Fair Value [Line Items]
Impairment charges				$ 1,597