Leases - Additional Information (Details) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 24, 2021 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) Agreement	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) Item
Operating Leased Assets [Line Items]
Variable lease revenues				$ 42,800	$ 41,800
Operating lease right-of-use asset		$ 41,577		41,577		$ 76,268
Payments to Tenant	$ 5,400
Lease liability - operating lease		39,743		39,743		88,816
Gain (loss) on termination of lease				3,615	0
Gain on disposition of properties		0	$ 24	10,521	509
Impairment charges		$ 9,925	$ 0	$ 9,925	$ 51,549
Lease agreement purchase price						$ 14,500
Minimum
Operating Leased Assets [Line Items]
Operating lease term		1 month		1 month
Minimum | Consolidated Total Revenues | Customer Concentration Risk
Operating Leased Assets [Line Items]
Concentration risk, percentage		10.00%	10.00%	10.00%	10.00%
Maximum
Operating Leased Assets [Line Items]
Operating lease term		60 years		60 years
991 Madison Avenue Manhattan, NY | Accounting Standards Update 2016-02
Operating Leased Assets [Line Items]
Capital lease term						49 years
Operating Lease term						15 years
1238 Wisconsin
Operating Leased Assets [Line Items]
Operating lease right-of-use asset						$ 1,900
Operating lease liability						1,900
Lease agreement purchase price						11,500
COVID-19
Operating Leased Assets [Line Items]
Impairment charges		$ 2,300		$ 2,300	$ 12,400
Number of rent concession agreements | Agreement				84
Number of rent concession agreements for rent deferral | Agreement				18
Number of rent concession agreements for rent abatements | Agreement				66
Number of rent concession agreements accounted as no change in contract | Agreement				16
Deferred receivables		6,400		$ 6,400
Rent abatements				3,000
Aggregate credit losses and rent abatements		$ (300)	$ 13,300	$ 3,400	$ 26,900
Pro rata core leased occupancy rate percentage				92.60%	91.10%
Pro rata fund leased occupancy rate percentage				90.00%	89.80%
Core Portfolio | COVID-19
Operating Leased Assets [Line Items]
Percentage of rent collections		97.10%		97.10%
Opportunity Funds | COVID-19
Operating Leased Assets [Line Items]
Percentage of rent collections		92.50%		92.50%
Fund IV Property
Operating Leased Assets [Line Items]
Operating lease right-of-use asset		$ 31,400		$ 31,400
Termination cost				3,600
Lease liability - operating lease		46,000		46,000
Building improvements and other assets		10,300		10,300
Gain (loss) on termination of lease				700
Gain on disposition of properties				200
Impairment charge of right-of-use asset						12,300
Rye Corporate Office Lease
Operating Leased Assets [Line Items]
Operating lease right-of-use asset		400		400
Operating lease liability		$ 400		$ 400
Office Lease
Operating Leased Assets [Line Items]
Operating lease right-of-use asset						1,700
Lease liability - operating lease						$ 1,700
Number of operating lease | Item						1
BSP II
Operating Leased Assets [Line Items]
Number of operating lease | Item						1
Branch Plaza
Operating Leased Assets [Line Items]
Number of operating lease | Item						1
Operating Lease term						22 years