Related Party Transactions - Aircraft Time Sharing Agreement (Details) - Related Party - Aircraft Time Sharing Agreement - Air Transportation Equipment $ in Millions		3 Months Ended
	Oct. 22, 2015 aircraft	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
DriveTime Automotive Group, Inc.
Related Party Transaction [Line Items]
Number of aircrafts | aircraft	2
Contractual agreement term	12 months
Number of allowable days prior to contract termination with written notice	30 days
Expenses from transactions with related party | $		$ 0.1	$ 0.1
Verde Investments, Inc.
Related Party Transaction [Line Items]
Contractual agreement, perpetual automatic renewal	12 months