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, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	[1]	$ 55.7	$ 8.2
Restricted cash and cash equivalents	[1]	338.0	255.6
Restricted securities available for sale	[2]	54.4	46.1
Loans receivable, net	[1]	5,444.1	4,741.5
Liabilities
Revolving secured line of credit	[1]	0.0	13.9
Secured financing	[1]	3,122.8	2,527.6
Senior notes	[1]	562.6	569.4
Carrying Amount [Member]
Assets
Cash and cash equivalents		55.7	8.2
Restricted cash and cash equivalents		338.0	255.6
Restricted securities available for sale		54.4	46.1
Loans receivable, net		5,344.4	4,619.6
Liabilities
Revolving secured line of credit		0.0	13.9
Secured financing		3,122.2	2,514.1
Senior notes		543.6	542.8
Estimated Fair Value [Member]
Assets
Cash and cash equivalents		55.7	8.2
Restricted cash and cash equivalents		338.0	255.6
Restricted securities available for sale		54.4	46.1
Loans receivable, net		5,444.1	4,741.5
Liabilities
Revolving secured line of credit		0.0	13.9
Secured financing		3,122.8	2,527.6
Senior notes		$ 562.6	$ 569.4

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

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