Related Party Transactions (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 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		0.40%		0.40%		0.40%
New Consumer Loan assignments				$ 943.6	$ 760.7
Accelerated Dealer Holdback payments		$ 12.8	$ 10.7	26.6	21.9
Dealer Holdback payments		37.5	33.3	78.6	67.8
Affiliated Dealer Activity [Member]
Related Party Transaction [Line Items]
Dealer Loan revenue		$ 0.5	$ 0.4	$ 0.9	$ 0.8
Dealer Loan revenue, percentage		0.30%	0.30%	0.30%	0.30%
New Consumer Loan assignments	[1]	$ 1.0	$ 1.0	$ 2.5	$ 2.1
New Consumer Loan assignments, percentage	[1]	0.20%	0.30%	0.20%	0.20%
Accelerated Dealer Holdback payments		$ 0.0	$ 0.1	$ 0.1	$ 0.1
Accelerated Dealer Holdback payments, percentage		0.00%	0.90%	0.40%	0.50%
Dealer Holdback payments		$ 0.4	$ 0.4	$ 0.7	$ 0.8
Dealer Holdback payments, percentage		1.10%	1.20%	0.90%	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.