Loans and Allowance for Credit Losses - Troubled Debt Restructurings, Excluding Loans Acquired, Segregated by Class of Loans (Details) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($) loan	Sep. 30, 2020 loan	Dec. 31, 2020 USD ($) loan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	1	5
Extended Maturity and Payment Deferral | COVID-19 Pandemic
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	35
Troubled debt, balance | $	$ 82,000
Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	47		54
Troubled debt, balance | $	$ 6,801		$ 7,513
Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	32		32
Troubled debt, balance | $	$ 4,251		$ 3,138
Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	15		22
Troubled debt, balance | $	$ 2,550		$ 4,375
Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	1	5
Real Estate | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	43		48
Troubled debt, balance | $	$ 4,956		$ 5,260
Real Estate | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	30		29
Troubled debt, balance | $	$ 3,814		$ 2,512
Real Estate | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	13		19
Troubled debt, balance | $	$ 1,142		$ 2,748
Real Estate | Single family residential
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications		5
Real Estate | Single family residential | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	40		46
Troubled debt, balance | $	$ 4,135		$ 5,199
Real Estate | Single family residential | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	28		28
Troubled debt, balance | $	$ 2,994		$ 2,463
Real Estate | Single family residential | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	12		18
Troubled debt, balance | $	$ 1,141		$ 2,736
Real Estate | Other commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	1
Real Estate | Other commercial | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	3		2
Troubled debt, balance | $	$ 821		$ 61
Real Estate | Other commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	2		1
Troubled debt, balance | $	$ 820		$ 49
Real Estate | Other commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	1		1
Troubled debt, balance | $	$ 1		$ 12
Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	4		6
Troubled debt, balance | $	$ 1,845		$ 2,253
Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	2		3
Troubled debt, balance | $	$ 437		$ 626
Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	2		3
Troubled debt, balance | $	$ 1,408		$ 1,627
Commercial | Commercial | Loans, Excluding Acquired Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	4		6
Troubled debt, balance | $	$ 1,845		$ 2,253
Commercial | Commercial | Loans, Excluding Acquired Loans | Accruing TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	2		3
Troubled debt, balance | $	$ 437		$ 626
Commercial | Commercial | Loans, Excluding Acquired Loans | Nonaccrual TDR Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of loan modifications	2		3
Troubled debt, balance | $	$ 1,408		$ 1,627