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, 2018		Dec. 31, 2017
Assets
Cash and cash equivalents	[1]	$ 195.7		$ 8.2
Restricted cash and cash equivalents	[1]	347.6		255.6
Restricted securities available for sale	[2]	56.7		46.1
Loans receivable, net	[1]	5,650.7		4,741.5
Liabilities
Revolving secured line of credit	[1]	0.0		13.9
Secured financing	[1]	3,321.5		2,527.6
Senior notes	[1]	564.9		569.4
Mortgage note		12.0	[1]	0.0
Carrying Amount [Member]
Assets
Cash and cash equivalents		195.7		8.2
Restricted cash and cash equivalents		347.6		255.6
Restricted securities available for sale		56.7		46.1
Loans receivable, net		5,557.6		4,619.6
Liabilities
Revolving secured line of credit		0.0		13.9
Secured financing		3,320.9		2,514.1
Senior notes		544.0		542.8
Mortgage note		12.0		0.0
Estimated Fair Value [Member]
Assets
Cash and cash equivalents		195.7		8.2
Restricted cash and cash equivalents		347.6		255.6
Restricted securities available for sale		56.7		46.1
Loans receivable, net		5,650.7		4,741.5
Liabilities
Revolving secured line of credit		0.0		13.9
Secured financing		3,321.5		2,527.6
Senior notes		564.9		569.4
Mortgage note		$ 12.0		$ 0.0

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