Leases - Additional Information (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) Agreement	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) Item
Operating Leased Assets [Line Items]
Variable lease revenues			$ 29,300	$ 27,300
Operating lease right-of-use asset	$ 42,398		42,398		$ 76,268
Lease liability - operating lease	40,861		40,861		88,816
Gain (loss) on termination of lease			3,615	0
Gain on disposition of properties	5,909	$ 485	10,521	485
Impairment charges	0	$ 0	0	$ 51,549
Lease agreement purchase price					$ 14,500
Minimum
Operating Leased Assets [Line Items]
Operating lease term		1 month		1 month
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			$ 12,400
Number of rent concession agreements | Agreement			74
Number of rent concession agreements for rent deferral | Agreement			17
Number of rent concession agreements for rent abatements | Agreement			57
Number of rent concession agreements accounted as no change in contract | Agreement			15
Deferred receivables	7,700		$ 7,700
Rent abatements			2,400
Aggregate credit losses and rent abatements	0	$ 9,400	$ 3,700	$ 13,700
Pro rata core leased occupancy rate percentage			92.40%	93.30%
Pro rata fund leased occupancy rate percentage			89.00%	91.10%
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