Fair Value of Financial Instruments (Schedule of Comparison of the Carrying Value and Estimated Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018
Assets
Cash and cash equivalents	[1]	$ 24.7	$ 25.7
Restricted cash and cash equivalents	[1]	329.8	303.6
Restricted securities available for sale	[2]	59.8	58.6
Loans receivable, net	[1]	6,647.0	5,855.1
Liabilities
Revolving secured line of credit	[1]	52.2	171.9
Secured financing	[1]	3,292.2	3,100.9
Senior notes	[1]	990.9	556.3
Mortgage note	[1]	11.5	11.9
Carrying Amount [Member]
Assets
Cash and cash equivalents		24.7	25.7
Restricted cash and cash equivalents		329.8	303.6
Restricted securities available for sale		59.8	58.6
Loans receivable, net		6,563.7	5,763.3
Liabilities
Revolving secured line of credit		52.2	171.9
Secured financing		3,228.3	3,092.7
Senior notes		940.2	544.4
Mortgage note		11.5	11.9
Estimated Fair Value [Member]
Assets
Cash and cash equivalents		24.7	25.7
Restricted cash and cash equivalents		329.8	303.6
Restricted securities available for sale		59.8	58.6
Loans receivable, net		6,647.0	5,855.1
Liabilities
Revolving secured line of credit		52.2	171.9
Secured financing		3,292.2	3,100.9
Senior notes		990.9	556.3
Mortgage note		$ 11.5	$ 11.9

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

[2] Measured at fair value on a recurring basis.