Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Additional Information (Details 2)	3 Months Ended
	Mar. 31, 2021 USD ($) KeyRatio	Mar. 31, 2020 USD ($)	Dec. 31, 2020 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
Exposure for commercial non accrual loans to be reviewed on individual basis	$ 500,000
Exposure for commercial accrual loans deemed to be reviewed on individual basis	500,000
LHFS past due 90 days or more	$ 109,600,000		$ 119,400,000
Percentage of outstanding principal to be repurchased under GNMA optional repurchase program	100.00%
Financing Receivable [Abstract]
PCL	$ (10,501,000)	$ 20,581,000
Allowance for Credit Losses, ACL [Member]
Financing Receivable [Abstract]
PCL	(10,501,000)	20,581,000
Commercial and Industrial Loans [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable [Abstract]
PCL	4,051,000	(2,024,000)
State and Other Political Subdivision Loans [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable [Abstract]
PCL	(175,000)	(1,243,000)
Other Commercial Loans [Member] | Allowance for Credit Losses, ACL [Member]
Financing Receivable [Abstract]
PCL	(1,243,000)	$ (1,150,000)
Minimum [Member]
Financing Receivable [Abstract]
Credit amount used as baseline in evaluating loan policy	$ 100,000