Loans and Leases and the Allowance for Credit Losses - Summary of Current, Past Due and Nonaccrual Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	$ 1,926,000	$ 2,166,000
Total	135,920,000	134,068,000
Current
Financing Receivable, Past Due [Line Items]
Loans	132,200,000	129,839,000
30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans	1,506,000	1,724,000
Accruing Loans Past Due 90 Days or More
Financing Receivable, Past Due [Line Items]
Loans	288,000	339,000
Commercial and industrial
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	810,000	670,000
Total	61,012,000	57,010,000
Commercial and industrial | Current
Financing Receivable, Past Due [Line Items]
Loans	59,926,000	56,091,000
Commercial and industrial | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans	265,000	238,000
Commercial and industrial | Accruing Loans Past Due 90 Days or More
Financing Receivable, Past Due [Line Items]
Loans	11,000	11,000
Commercial Real Estate | Commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	578,000	869,000
Total	22,371,000	25,277,000
Commercial Real Estate | Commercial | Current
Financing Receivable, Past Due [Line Items]
Loans	21,560,000	24,072,000
Commercial Real Estate | Commercial | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans	231,000	311,000
Commercial Real Estate | Commercial | Accruing Loans Past Due 90 Days or More
Financing Receivable, Past Due [Line Items]
Loans	2,000	25,000
Commercial Real Estate | Residential builder and developer
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	2,000	3,000
Total	992,000	1,073,000
Commercial Real Estate | Residential builder and developer | Current
Financing Receivable, Past Due [Line Items]
Loans	981,000	1,065,000
Commercial Real Estate | Residential builder and developer | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans	9,000	5,000
Commercial Real Estate | Residential builder and developer | Accruing Loans Past Due 90 Days or More
Financing Receivable, Past Due [Line Items]
Loans	0	0
Commercial Real Estate | Other commercial construction
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	84,000	171,000
Total	5,320,000	6,653,000
Commercial Real Estate | Other commercial construction | Current
Financing Receivable, Past Due [Line Items]
Loans	5,123,000	6,322,000
Commercial Real Estate | Other commercial construction | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans	113,000	159,000
Commercial Real Estate | Other commercial construction | Accruing Loans Past Due 90 Days or More
Financing Receivable, Past Due [Line Items]
Loans	0	1,000
Residential Real Estate | Residential
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	219,000	215,000
Total	22,196,000	22,353,000
Residential Real Estate | Residential | Current
Financing Receivable, Past Due [Line Items]
Loans	21,042,000	21,080,000
Total	21,042,000	21,080,000
Residential Real Estate | Residential | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans	667,000	763,000
Residential Real Estate | Residential | Accruing Loans Past Due 90 Days or More
Financing Receivable, Past Due [Line Items]
Loans	268,000	295,000
Total	268,000	295,000
Residential Real Estate | Residential — limited documentation
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	57,000	55,000
Total	823,000	911,000
Residential Real Estate | Residential — limited documentation | Current
Financing Receivable, Past Due [Line Items]
Loans	737,000	825,000
Total	737,000	825,000
Residential Real Estate | Residential — limited documentation | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans	29,000	31,000
Residential Real Estate | Residential — limited documentation | Accruing Loans Past Due 90 Days or More
Financing Receivable, Past Due [Line Items]
Loans	0	0
Total	0	0
Consumer: | Home equity lines and loans
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	82,000	81,000
Total	4,576,000	4,649,000
Consumer: | Home equity lines and loans | Current
Financing Receivable, Past Due [Line Items]
Loans	4,464,000	4,528,000
Total	4,464,000	4,528,000
Consumer: | Home equity lines and loans | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans	30,000	40,000
Consumer: | Home equity lines and loans | Accruing Loans Past Due 90 Days or More
Financing Receivable, Past Due [Line Items]
Loans	0	0
Total	0	0
Consumer: | Recreational finance
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	28,000	36,000
Total	11,739,000	10,058,000
Consumer: | Recreational finance | Current
Financing Receivable, Past Due [Line Items]
Loans	11,621,000	9,935,000
Total	11,621,000	9,935,000
Consumer: | Recreational finance | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans	90,000	87,000
Consumer: | Recreational finance | Accruing Loans Past Due 90 Days or More
Financing Receivable, Past Due [Line Items]
Loans	0	0
Total	0	0
Consumer: | Automobile
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	11,000	14,000
Total	4,743,000	3,992,000
Consumer: | Automobile | Current
Financing Receivable, Past Due [Line Items]
Loans	4,680,000	3,918,000
Total	4,680,000	3,918,000
Consumer: | Automobile | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans	52,000	60,000
Consumer: | Automobile | Accruing Loans Past Due 90 Days or More
Financing Receivable, Past Due [Line Items]
Loans	0	0
Total	0	0
Consumer: | Other
Financing Receivable, Past Due [Line Items]
Nonaccrual loans	55,000	52,000
Total	2,148,000	2,092,000
Consumer: | Other | Current
Financing Receivable, Past Due [Line Items]
Loans	2,066,000	2,003,000
Consumer: | Other | 30-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans	20,000	30,000
Consumer: | Other | Accruing Loans Past Due 90 Days or More
Financing Receivable, Past Due [Line Items]
Loans	$ 7,000	$ 7,000