Commitments and Contingencies - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) property	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) property	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Number of properties subject to ground leases | property	10		10
Number ground leases acquired | property	2
Operating lease right-of-use asset (Note 9)	$ 56,229		$ 56,229		$ 50,211
Operating lease liability (Note 9)	$ 24,458		$ 24,458		$ 23,985
Weighted average remaining lease term	32 years 3 months 18 days		32 years 3 months 18 days
Weighted average discount rate	4.33%		4.33%
Payments	$ 400		$ 1,100
Expense	$ 300	$ 300	$ 1,000	$ 1,000
Legal settlement reserve						$ 7,400
Asset management fees | Service Provider | Defendants vs. Service Providers
Loss Contingencies [Line Items]
Legal expenses				$ 1,000
Minimum
Loss Contingencies [Line Items]
Term of contract	15 years		15 years
Maximum
Loss Contingencies [Line Items]
Term of contract	97 years		97 years