Related Party Transactions (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Affiliated Dealer Loan balances		$ 12.6	$ 8.7
Percentage of Affiliated Dealer Loan balances		0.40%
New Consumer Loan assignments		$ 1,795.1	1,471.4	$ 1,356.6
Accelerated Dealer Holdback payments		52.6	41.7	40.4
Dealer Holdback payments		150.1	135.5	114.2
Affiliated Dealer Activity [Member]
Related Party Transaction [Line Items]
Dealer Loan revenue		$ 2.5	$ 1.6	$ 1.5
Dealer Loan revenue, percentage		0.40%	0.30%	0.30%
New Consumer Loan assignments	[1]	$ 5.9	$ 4.2	$ 4.3
New Consumer Loan assignments, percentage		0.30%	0.30%	0.30%
Accelerated Dealer Holdback payments		$ 0.2	$ 0.1	$ 0.1
Accelerated Dealer Holdback payments, percentage		0.40%	0.20%	0.20%
Dealer Holdback payments		$ 1.4	$ 1.4	$ 2.2
Dealer Holdback payments, percentage		0.90%	1.00%	1.90%

[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.