Loans Held for Investment and Allowance for Loan Losses (Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unpaid principal balance	$ 992,595	$ 936,239
Net deferred origination costs	18,349	16,557
Total loans held for investment	1,010,944	952,796
Term loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unpaid principal balance	847,403	804,227
Lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total unpaid principal balance	$ 145,192	$ 132,012