Related Party Transactions (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Related Party Transaction [Line Items]
Affiliated Dealer Loan balances		$ 16.8		$ 16.8		$ 12.6
Percentage of Affiliated Dealer Loan balances		0.60%		0.60%		0.40%
New Consumer Loan assignments				$ 1,000.7	$ 943.6
Accelerated Dealer Holdback payments		$ 14.9	$ 12.8	29.7	26.6
Dealer Holdback payments		35.9	37.5	75.8	78.6
Affiliated Dealer Activity [Member]
Related Party Transaction [Line Items]
Dealer Loan revenue		$ 0.8	$ 0.5	$ 1.5	$ 0.9
Dealer Loan revenue, percentage		0.40%	0.30%	0.40%	0.30%
New Consumer Loan assignments	[1]	$ 4.3	$ 1.0	$ 8.9	$ 2.5
New Consumer Loan assignments, percentage	[1]	0.70%	0.20%	0.60%	0.20%
Accelerated Dealer Holdback payments		$ 0.1		$ 0.2	$ 0.1
Accelerated Dealer Holdback payments, percentage		0.70%	0.00%	0.70%	0.40%
Dealer Holdback payments		$ 0.3	$ 0.4	$ 0.6	$ 0.7
Dealer Holdback payments, percentage		0.80%	1.10%	0.80%	0.90%

[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.