Debt - Warehouse Borrowings (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Warehouse Borrowings [Abstract]
Maximum Borrowing Capacity	$ 1,000,000
Balance Outstanding	315,152	$ 575,363
Repurchase agreement 1
Warehouse Borrowings [Abstract]
Maximum Borrowing Capacity	150,000
Balance Outstanding	96,739	100,630
Repurchase agreement 2
Warehouse Borrowings [Abstract]
Maximum Borrowing Capacity	50,000
Balance Outstanding	27,802	31,632
Repurchase agreement 3
Warehouse Borrowings [Abstract]
Maximum Borrowing Capacity	225,000
Balance Outstanding	73,162	154,020
Finance receivables made to warehouse customers	700	41,800
Repurchase agreement 4
Warehouse Borrowings [Abstract]
Maximum Borrowing Capacity	250,000
Balance Outstanding	71,774	152,772
Repurchase agreement 5
Warehouse Borrowings [Abstract]
Maximum Borrowing Capacity	175,000
Balance Outstanding	30,511	88,920
Repurchase agreement 6
Warehouse Borrowings [Abstract]
Maximum Borrowing Capacity	100,000
Balance Outstanding	14,419	$ 47,389
Repurchase agreement 7
Warehouse Borrowings [Abstract]
Maximum Borrowing Capacity	50,000
Balance Outstanding	$ 745