Related Party Transactions (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Related Party Transaction [Line Items]
Affiliated Dealer Loan balances		$ 9.5		$ 9.5		$ 8.7
Percentage of Affiliated Dealer Loan balances		0.30%		0.30%		0.40%
New Consumer Loan assignments				$ 1,371.5	$ 1,103.6
Accelerated Dealer Holdback payments		$ 13.0	$ 9.7	39.6	31.6
Dealer Holdback payments		36.6	33.7	115.2	101.5
Affiliated Dealer Activity [Member]
Related Party Transaction [Line Items]
Dealer Loan revenue		$ 0.5	$ 0.4	$ 1.4	$ 1.2
Dealer Loan revenue, percentage		0.30%	0.30%	0.30%	0.30%
New Consumer Loan assignments	[1]	$ 1.1	$ 0.9	$ 3.6	$ 3.0
New Consumer Loan assignments, percentage	[1]	0.20%	0.20%	0.20%	0.20%
Accelerated Dealer Holdback payments		$ 0.0		$ 0.1	$ 0.1
Accelerated Dealer Holdback payments, percentage		0.00%	0.00%	0.30%	0.30%
Dealer Holdback payments		$ 0.3	$ 0.3	$ 1.0	$ 1.1
Dealer Holdback payments, percentage		0.80%	0.90%	0.90%	1.10%

[1] Represents advances paid to Dealers on Consumer Loans assigned under our Portfolio Program and one-time payments made to Dealers to purchase Consumer Loans assigned under our Purchase Program.