Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Additional Information (Details 2)	3 Months Ended
	Mar. 31, 2019 USD ($) KeyRatio LoanPool CreditRiskGrade	Dec. 31, 2018 USD ($)
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	$ 40,800,000	$ 37,400,000
Percentage of outstanding principal to be repurchased under GNMA optional repurchase program	100.00%
Financing Receivable [Abstract]
Number of primary commercial loan groups | LoanPool	9
Number of individual credit risk grades | CreditRiskGrade	10
Minimum [Member]
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