Loans Held for Investment, Allowance for Loan Losses and Loans Held for Sale (Loans) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unpaid principal balance	$ 936,239	$ 980,451
Net deferred origination costs	16,557	19,994
Total loans held for investment	952,796	1,000,445
Term loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unpaid principal balance	804,227	864,066
Lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unpaid principal balance	$ 132,012	$ 116,385