Fair Value of Financial Instruments (Schedule of Comparison of the Carrying Value and Estimated Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions		Jun. 30, 2019	Dec. 31, 2018
Assets
Cash and cash equivalents	[1]	$ 19.7	$ 25.7
Restricted cash and cash equivalents	[1]	328.8	303.6
Restricted securities available for sale	[2]	61.5	58.6
Loans receivable, net	[1]	6,466.8	5,855.1
Liabilities
Revolving secured line of credit	[1]	38.4	171.9
Secured financing	[1]	3,275.6	3,100.9
Senior notes	[1]	985.2	556.3
Mortgage note	[1]	11.6	11.9
Carrying Amount [Member]
Assets
Cash and cash equivalents		19.7	25.7
Restricted cash and cash equivalents		328.8	303.6
Restricted securities available for sale		61.5	58.6
Loans receivable, net		6,384.0	5,763.3
Liabilities
Revolving secured line of credit		38.4	171.9
Secured financing		3,233.0	3,092.7
Senior notes		939.6	544.4
Mortgage note		11.6	11.9
Estimated Fair Value [Member]
Assets
Cash and cash equivalents		19.7	25.7
Restricted cash and cash equivalents		328.8	303.6
Restricted securities available for sale		61.5	58.6
Loans receivable, net		6,466.8	5,855.1
Liabilities
Revolving secured line of credit		38.4	171.9
Secured financing		3,275.6	3,100.9
Senior notes		985.2	556.3
Mortgage note		$ 11.6	$ 11.9

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

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