Goodwill and Other Intangibles - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020		Jan. 31, 2021
Goodwill [Line Items]
Goodwill	$ 26,826		$ 26,826		$ 19,620	[1]
Amortization of intangibles	500	$ 232	1,406	$ 608
Mortgage servicing asset	15,000		15,000		7,100
Loan Servicing Assets Included in Other Amortization Intangibles [Member]
Goodwill [Line Items]
Accumulated amortization of intangibles	258		258		209
Loan Servicing Assets Included in Interest and Fees on Loans [Member]
Goodwill [Line Items]
Amortization of intangibles			$ 131		$ 189
Bay Banks [Member]
Goodwill [Line Items]
Goodwill							$ 7,206
Bay Banks [Member] | Core Deposits [Member]
Goodwill [Line Items]
Amortization of intangible assets			10 years
Net assets acquired	$ 6,900		$ 6,900
Minimum [Member]
Goodwill [Line Items]
Amortization of intangible assets			5 years
Maximum [Member]
Goodwill [Line Items]
Amortization of intangible assets			12 years

[1] Derived from audited December 31, 2020 Consolidated Financial Statements.