Segment Information - Information about Company's Segments (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Taxable-equivalent adjustment	$ 13,886,000	$ 10,726,000	$ 27,348,000	$ 13,960,000
Average total assets	203,492,000	180,414,000	203,492,000	180,414,000	$ 190,252,000
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Average total assets	49,166,000	35,696,000	49,166,000	35,696,000	40,930,000
Hospitality [Member]
Segment Reporting Information [Line Items]
Average total assets		1,250,000		1,250,000
Retail Banking [Member]
Segment Reporting Information [Line Items]
Average total assets	21,322,000	19,690,000	21,322,000	19,690,000	20,312,000
Retail Banking [Member] | Peoples United Financial Inc [Member]
Segment Reporting Information [Line Items]
Average total assets		4,720,000		4,720,000
Other Segments [Member]
Segment Reporting Information [Line Items]
Average total assets	$ 39,446,000	47,374,000	$ 39,446,000	47,374,000	$ 44,171,000
Other Segments [Member] | Peoples United Financial Inc [Member]
Segment Reporting Information [Line Items]
Average total assets		$ 591,000		$ 591,000