Loans Held for Investment - By Region (Details)	Dec. 31, 2018	Dec. 31, 2017
Loans held for investment by Region [Line Items]
Percentage of Loans concentrated in major states	39.90%	40.40%
New York
Loans held for investment by Region [Line Items]
Percentage of Loans held in state	10.30%	10.50%
California
Loans held for investment by Region [Line Items]
Percentage of Loans held in state	9.30%	9.30%
Pennsylvania
Loans held for investment by Region [Line Items]
Percentage of Loans held in state	8.50%	8.50%
New Jersey
Loans held for investment by Region [Line Items]
Percentage of Loans held in state	6.80%	6.90%
Illinois
Loans held for investment by Region [Line Items]
Percentage of Loans held in state	5.00%	5.20%