Fair Value of Financial Instruments (Schedule of Assets and Liabilities, Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	[1]	$ 11.5	$ 8.2
Restricted cash and cash equivalents	[1]	368.5	255.6
Restricted securities available for sale	[2]	51.3	46.1
Loans receivable, net	[1]	5,170.6	4,741.5
Revolving secured line of credit	[1]	23.0	13.9
Secured financing	[1]	2,878.8	2,527.6
Senior notes	[1]	562.9	569.4
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	[1]	11.5	8.2
Restricted cash and cash equivalents	[1]	368.5	255.6
Restricted securities available for sale	[2]	41.2	37.1
Revolving secured line of credit	[1]	23.0	13.9
Senior notes	[1]	562.9	569.4
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted securities available for sale	[2]	10.1	9.0
Revolving secured line of credit	[1]	0.0	0.0
Secured financing	[1]	2,878.8	2,527.6
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans receivable, net	[1]	$ 5,170.6	$ 4,741.5

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

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