Related Party Transactions (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Affiliated Dealer Loan balances		$ 1.4	$ 12.6
Percentage of Affiliated Dealer Loan balances		0.00%	0.40%
New Consumer Loan assignments		$ 1,881.3	$ 1,795.1	$ 1,471.4
Accelerated Dealer Holdback payments		53.6	52.6	41.7
Dealer Holdback payments		142.0	150.1	135.5
Affiliated Dealer Activity [Member]
Related Party Transaction [Line Items]
Dealer Loan revenue		$ 1.5	$ 2.5	$ 1.6
Dealer Loan revenue, percentage		0.20%	0.40%	0.30%
New Consumer Loan assignments	[1]	$ 8.9	$ 5.9	$ 4.2
New Consumer Loan assignments, percentage		0.30%	0.30%	0.30%
Accelerated Dealer Holdback payments		$ 0.2	$ 0.2	$ 0.1
Accelerated Dealer Holdback payments, percentage		0.40%	0.40%	0.20%
Dealer Holdback payments		$ 1.0	$ 1.4	$ 1.4
Dealer Holdback payments, percentage		0.70%	0.90%	1.00%

[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.