Fair Value of Financial Instruments (Schedule of Comparison of the Carrying Value and Estimated Fair Value of Financial Instruments) - USD ($) $ in Millions		Sep. 30, 2021	Dec. 31, 2020
Assets
Cash and cash equivalents	[1]	$ 13.3	$ 16.0
Restricted cash and cash equivalents	[1]	429.0	380.2
Debt Securities, Available-for-sale, Restricted		67.1	66.1
Loans receivable, net	[1]	6,833.9	7,216.4
Liabilities
Revolving secured line of credit	[1]	72.2	95.9
Secured financing	[1]	3,783.0	3,793.9
Senior notes	[1]	834.6	842.0
Mortgage note	[1]	9.9	10.5
Carrying Amount [Member]
Assets
Cash and cash equivalents		13.3	16.0
Restricted cash and cash equivalents		429.0	380.2
Debt Securities, Available-for-sale, Restricted		67.1	66.1
Loans receivable, net		6,582.6	6,787.9
Liabilities
Revolving secured line of credit		72.2	95.9
Secured financing		3,733.0	3,711.6
Senior notes		792.0	790.6
Mortgage note		9.9	10.5
Estimated Fair Value [Member]
Assets
Cash and cash equivalents		13.3	16.0
Restricted cash and cash equivalents		429.0	380.2
Debt Securities, Available-for-sale, Restricted		67.1	66.1
Loans receivable, net		6,833.9	7,216.4
Liabilities
Revolving secured line of credit		72.2	95.9
Secured financing		3,783.0	3,793.9
Senior notes		834.6	842.0
Mortgage note		$ 9.9	$ 10.5

[1] Measured at amortized cost with fair value disclosed.