Operating Leases - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) lease numberOfRenewals	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) lease numberOfRenewals	Sep. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Rental income			$ 234.9	$ 212.8
Weighted average remaining lease term	80 years 3 months 18 days		80 years 3 months 18 days
Operating lease costs	$ 0.9	$ 0.7	$ 2.8	1.9
Cash paid for operating lease liabilities	$ 0.4	$ 0.3	$ 1.2	$ 0.8
Chicago Illinois Office
Lessee, Lease, Description [Line Items]
Weighted average remaining lease term	5 years		5 years
Arizona
Lessee, Lease, Description [Line Items]
Number of parcels of land | lease	3		3
Options to renew | numberOfRenewals	0		0