Related Party Transactions (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Related Party Transaction [Line Items]
Affiliated Dealer Loan balances		$ 18.5		$ 18.5		$ 12.6
Percentage of Affiliated Dealer Loan balances		0.60%		0.60%		0.40%
New Consumer Loan assignments				$ 1,476.4	$ 1,371.5
Accelerated Dealer Holdback payments		$ 13.7	$ 13.0	43.4	39.6
Dealer Holdback payments		33.9	36.6	109.7	115.2
Affiliated Dealer Activity [Member]
Related Party Transaction [Line Items]
Dealer Loan revenue		$ 0.9	$ 0.5	$ 2.4	$ 1.4
Dealer Loan revenue, percentage		0.50%	0.30%	0.40%	0.30%
New Consumer Loan assignments	[1]	$ 4.7	$ 1.1	$ 13.6	$ 3.6
New Consumer Loan assignments, percentage	[1]	0.70%	0.20%	0.70%	0.20%
Accelerated Dealer Holdback payments		$ 0.1		$ 0.3	$ 0.1
Accelerated Dealer Holdback payments, percentage		0.70%	0.00%	0.70%	0.30%
Dealer Holdback payments		$ 0.3	$ 0.3	$ 0.9	$ 1.0
Dealer Holdback payments, percentage		0.90%	0.80%	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.