Loans Held for Investment and Allowance for Loan Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unpaid principal balance	$ 940,880	$ 980,451
Net deferred origination costs	16,323	19,994
Total loans held for investment	957,203	1,000,445
Term loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unpaid principal balance	815,043	864,066
Lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unpaid principal balance	$ 125,837	$ 116,385