Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Net Income (Loss)	$ 721,000	$ 690,000	$ 1,907,000	$ 2,259,000
Total Average Assets	209,581,000	205,791,000	211,008,000	204,266,000
Operating Segments
Segment Reporting Information [Line Items]
Total Revenues	2,332,000	2,335,000	6,894,000	7,343,000
Inter- segment Revenues
Segment Reporting Information [Line Items]
Total Revenues	0	0	0	0
Commercial Bank
Segment Reporting Information [Line Items]
Net Income (Loss)	239,000	251,000	645,000	819,000
Total Average Assets	80,434,000	80,473,000	80,903,000	80,169,000
Commercial Bank | Operating Segments
Segment Reporting Information [Line Items]
Total Revenues	723,000	738,000	2,139,000	2,308,000
Commercial Bank | Inter- segment Revenues
Segment Reporting Information [Line Items]
Total Revenues	0	1,000	4,000	4,000
Retail Bank
Segment Reporting Information [Line Items]
Net Income (Loss)	446,000	473,000	1,364,000	1,400,000
Total Average Assets	53,128,000	51,024,000	52,771,000	51,124,000
Retail Bank | Operating Segments
Segment Reporting Information [Line Items]
Total Revenues	1,292,000	1,307,000	3,854,000	3,837,000
Retail Bank | Inter- segment Revenues
Segment Reporting Information [Line Items]
Total Revenues	0	0	0	0
Institutional Services and Wealth Management
Segment Reporting Information [Line Items]
Net Income (Loss)	137,000	120,000	409,000	515,000
Total Average Assets	3,898,000	3,664,000	3,735,000	3,680,000
Institutional Services and Wealth Management | Operating Segments
Segment Reporting Information [Line Items]
Total Revenues	389,000	363,000	1,167,000	1,344,000
Institutional Services and Wealth Management | Inter- segment Revenues
Segment Reporting Information [Line Items]
Total Revenues	4,000	3,000	10,000	9,000
All Other
Segment Reporting Information [Line Items]
Net Income (Loss)	(101,000)	(154,000)	(511,000)	(475,000)
Total Average Assets	72,121,000	70,630,000	73,599,000	69,293,000
All Other | Operating Segments
Segment Reporting Information [Line Items]
Total Revenues	(72,000)	(73,000)	(266,000)	(146,000)
All Other | Inter- segment Revenues
Segment Reporting Information [Line Items]
Total Revenues	$ (4,000)	$ (4,000)	$ (14,000)	$ (13,000)