Leases - Schedule of right-of-use assets and lease liabilities related to ground leases (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Key Terms:
Weighted-average remaining lease term (years)	68 years 8 months 12 days	69 years 4 months 24 days
Weighted-average discount rate	7.79%	8.05%
Ground
Assets:
Right-of-use assets, at fair value	$ 38.2	$ 36.8
Liabilities:
Ground lease liabilities, at fair value	$ 38.2	$ 36.8