Business Combinations - Summary of Estimated Fair Value Adjustments of Consideration Paid, Acquired Asset and Assumed Liabilities (Detail) - USD ($)	1 Months Ended	9 Months Ended
	Jan. 31, 2021	Sep. 30, 2020	Sep. 30, 2021	Dec. 31, 2020	[1]
Consideration paid:
Effective settlement of subordinated notes		$ (349,000)
Fair value of liabilities assumed:
Goodwill			$ 26,826,000	$ 19,620,000
Bay Banks [Member]
Consideration paid:
Company's common shares issued	9,951,743
Purchase price per share	$ 12.55
Value of common stock issued	$ 124,928,000
Estimated fair value of common stock	472,000
Cash in lieu of fractional shares	3,400
Total consideration paid	125,403,000
Effective settlement of subordinated notes	(650,000)
Total consideration paid less effective settlement of subordinated notes	124,753,000
Fair value of assets acquired:
Cash and due from banks	44,066,000
Federal funds sold	1,732,000
Certificates of deposit	1,018,000
Securities available for sale	79,505,000
Restricted securities	4,385,000
Loans held for investment	1,030,433,000
Loans held for sale	3,814,000
Premises and equipment	15,532,000
Right-of-use asset	1,864,000
Other real estate owned	598,000
Bank owned life insurance	20,259,000
Mortgage servicing rights	987,000
Core deposit intangible	6,850,000
Deferred tax asset, net	2,685,000
Other assets	10,855,000
Total assets	1,224,583,000
Fair value of liabilities assumed:
Deposits	1,030,888,000
FHLB borrowings	10,124,000
FRB borrowings	24,815,000
Subordinated notes	31,850,000
Other liabilities	9,359,000
Total liabilities	1,107,036,000
Net identifiable assets acquired at fair value	117,547,000
Goodwill	$ 7,206,000

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