Loans Held for Investment and Allowance for Loan Losses (Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unpaid principal balance	$ 1,026,586	$ 936,239
Net deferred origination costs	20,002	16,557
Total loans held for investment	1,046,588	952,796
Term loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unpaid principal balance	871,956	804,227
Lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unpaid principal balance	$ 154,630	$ 132,012