Fair Value of Financial Instruments (Schedule of Assets and Liabilities, Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions		Sep. 30, 2018		Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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
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
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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]	44.8		37.1
Senior notes	[1]	564.9		569.4
Mortgage note	[1]	0.0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted securities available for sale	[2]	11.9		9.0
Revolving secured line of credit	[1]	0.0		13.9
Secured financing	[1]	3,321.5		2,527.6
Mortgage note	[1]	12.0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans receivable, net	[1]	$ 5,650.7		$ 4,741.5

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