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Description of Business (Percentage of Consumer Loans Assigned Based on Volumes) (Details) | 3 Months Ended
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Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016
Portfolio Program [Member] |  |  |  |  |  |  |  |
Description Of Business [Line Items] |  |  |  |  |  |  |  |
Percentage of new consumer loans unit volume |  | 71.90% | 72.30% | 73.30% | 76.90% | 76.20% | 77.80% | 82.40%
Percentage of new consumer loans dollar volume | [1] | 68.60% | 67.90% | 67.80% | 71.10% | 68.50% | 69.80% | 75.60%
Purchase Program [Member] |  |  |  |  |  |  |  |
Description Of Business [Line Items] |  |  |  |  |  |  |  |
Percentage of new consumer loans unit volume |  | 28.10% | 27.70% | 26.70% | 23.10% | 23.80% | 22.20% | 17.60%
Percentage of new consumer loans dollar volume | [1] | 31.40% | 32.10% | 32.20% | 28.90% | 31.50% | 30.20% | 24.40%
[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. Payments of Dealer Holdback and accelerated Dealer Holdback are not included.

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