Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
DriveTime Automotive Group, Inc. \| Related Party \| Master Dealer Agreement
Related Party Transaction [Line Items]
Ending receivables, related to excess cash flow from contracts	$ 6.0	$ 1.9

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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