Related Party Transactions - Notes Receivable (Details) - Affiliated Entity - Master Trust 2014 Series 2017-1
$ in Millions
12 Months Ended
Dec. 31, 2018
USD ($)
Related Party Transaction [Line Items]  
Percentage of economic interest 5.00%
Notes receivable from related parties $ 33.5
Interest income earned from related parties note $ 0.9
Weighted average stated interest rate of loans receivable 4.60%
Remaining term of loans receivable 4 years