Fair Value of Financial Instruments (Schedule of Assets and Liabilities, Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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
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
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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]	43.1	37.1
Revolving secured line of credit	[1]		13.9
Senior notes	[1]	562.6	569.4
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted securities available for sale	[2]	11.3	9.0
Revolving secured line of credit	[1]	0.0	0.0
Secured financing	[1]	3,122.8	2,527.6
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans receivable, net	[1]	$ 5,444.1	$ 4,741.5

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

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