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, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents		$ 4.9	$ 14.6
Restricted cash and cash equivalents		273.6	224.7
Restricted securities available for sale	[1]	46.1	45.3
Loans receivable, net		4,536.9	3,955.9
Liabilities
Revolving secured line of credit		130.5	0.0
Secured financing		2,348.5	2,072.0
Senior notes		569.0	560.5
Carrying Amount [Member]
Assets
Cash and cash equivalents		4.9	14.6
Restricted cash and cash equivalents		273.6	224.7
Restricted securities available for sale		46.1	45.3
Loans receivable, net		4,451.4	3,886.6
Liabilities
Revolving secured line of credit		130.5	0.0
Secured financing	[1]	2,327.9	2,062.4
Senior notes	[1]	542.4	541.3
Estimated Fair Value [Member]
Assets
Cash and cash equivalents		4.9	14.6
Restricted cash and cash equivalents		273.6	224.7
Restricted securities available for sale		46.1	45.3
Loans receivable, net		4,536.9	3,955.9
Liabilities
Revolving secured line of credit		130.5	0.0
Secured financing	[1]	2,348.5	2,072.0
Senior notes	[1]	$ 569.0	$ 560.5

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