Related Party Transactions (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Related Party Transaction [Line Items]
Affiliated Dealer Loan balances		$ 0.0		$ 0.0		$ 1.4
Percentage of Affiliated Dealer Loan balances		0.00%		0.00%		0.00%
New Consumer Loan assignments				$ 1,467.2	$ 1,476.4
Accelerated Dealer Holdback payments		$ 11.9	$ 13.7	35.5	43.4
Dealer Holdback payments		$ 32.1	33.9	$ 100.8	109.7
Affiliated Dealer Activity [Member]
Related Party Transaction [Line Items]
Dealer Loan revenue	[1]		$ 0.0		$ 1.2
Dealer Loan revenue, percentage	[1]		0.00%		0.20%
New Consumer Loan assignments	[1],[2]		$ 0.0		$ 8.9
New Consumer Loan assignments, percentage	[1],[2]		0.00%		0.40%
Accelerated Dealer Holdback payments	[1]		$ 0.0		$ 0.2
Accelerated Dealer Holdback payments, percentage	[1]		0.00%		0.50%
Dealer Holdback payments	[1]		$ 0.2		$ 0.8
Dealer Holdback payments, percentage	[1]		0.60%		0.70%

[1] We have reclassified related party transactions to reflect the June 2016 sale of certain affiliated Dealers by our founder, significant shareholder and former Chairman of the Board.

[2] 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.