Loans Held for Investment and Allowance for Loan Losses (Aging Analysis of Term Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-delinquent loans	$ 922,921	$ 890,297
Total unpaid principal balance	1,026,158	980,451
1-14 calendar days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans	23,340	25,899
15-29 calendar days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans	17,568	15,990
30-59 calendar days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans	28,503	22,677
60-89 calendar days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans	20,676	13,952
90 calendar days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past due loans	$ 13,150	$ 11,636