Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Additional Information (Details 2)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2015 USD ($)	Sep. 30, 2016 USD ($) KeyRatio LoanPool CreditRiskGrade	Dec. 31, 2015 USD ($)
Financing Receivable, Recorded Investment, Aging [Abstract]
Number of days used as baseline in evaluating collateral documentation exceptions for loan policy		90 days
Number of key quality ratios | KeyRatio		6
LHFS past due 90 days or more		$ 25,600,000	$ 21,800,000
Percentage of outstanding principal to be repurchased under GNMA optional repurchase program		100.00%
Amount of delinquent loans repurchased	$ 28,500,000
Repurchase gain included in gain on sales of loans			$ 304,000
Financing Receivable [Abstract]
Number of primary commercial loan groups | LoanPool		9
Number of individual credit risk grades | CreditRiskGrade		10
Minimum [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Loan amount used as baseline in credit quality review for loan policy		$ 1,000,000
Financing Receivable [Abstract]
Period to conduct asset review		6 months
Credit amount used as baseline in evaluating loan policy		$ 100,000
Maximum [Member]
Financing Receivable [Abstract]
Period to conduct asset review		18 months