Leases - Ground Leases (Details) ft² in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) ft² Lease property	Mar. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Number of properties subject to ground leases | property	104
Square feet subject to ground leases | ft²	8.7
Number of prepaid ground leases	42
Amortization of prepaid rent | $	$ 0.2	$ 0.1
Number of non-prepaid ground leases	62
Minimum
Lessee, Lease, Description [Line Items]
Ground lease, initial term	40 years
Maximum
Lessee, Lease, Description [Line Items]
Ground lease, initial term	99 years