Loans Held for Investment and Allowance for Loan Losses (Aging Analysis of Term Loans) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-delinquent loans	$ 859,904	$ 890,297
Total unpaid principal balance	953,809	980,451
1-14 calendar days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans	24,805	25,899
15-29 calendar days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans	12,263	15,990
30-59 calendar days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans	25,322	22,677
60-89 calendar days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans	19,226	13,952
90 calendar days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans	$ 12,289	$ 11,636