Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Related Party Transaction [Line Items]
Affiliated Dealer Loan balances	$ 9.2				$ 8.7
Percentage of Affiliated Dealer Loan balances	0.40%				0.40%
New Consumer Loan assignments	533.5		421.3
Accelerated Dealer Holdback payments	13.8		11.2
Dealer Holdback payments	41.1		34.5
Affiliated Dealer Activity [Member]
Related Party Transaction [Line Items]
Dealer Loan revenue	0.4		0.4
Dealer Loan revenue, percentage	0.30%		0.30%
New Consumer Loan assignments	1.5	[1]	1.1	[1]
New Consumer Loan assignments, percentage	0.20%	[1]	0.20%	[1]
Accelerated Dealer Holdback payments	0.1
Accelerated Dealer Holdback payments, percentage	0.70%		0.00%
Dealer Holdback payments	$ 0.3		$ 0.4
Dealer Holdback payments, percentage	0.70%		1.20%

[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.