Leases - Ground Leases (Details) ft² in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) property lease	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) ft² lease property	Sep. 30, 2020 USD ($)
Lessee, Lease, Description [Line Items]
Number of properties subject to ground leases | property	110		110
Square feet subject to ground leases | ft²			9.2
Number of prepaid ground leases			43
Amortization of prepaid rent | $	$ 0.1	$ 0.1	$ 0.4	$ 0.5
Number of non-prepaid ground leases	67		67
Minimum
Lessee, Lease, Description [Line Items]
Ground lease, initial term	40 years		40 years
Maximum
Lessee, Lease, Description [Line Items]
Ground lease, initial term	99 years		99 years