Allowance for Credit Losses and Credit Quality of Loans, Summary (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Dec. 31, 2022	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Allowance for Credit Losses [Abstract]
Allowance for credit losses	$ 114,601	$ 114,601	$ 100,800	$ 100,400		$ 96,800	$ 93,600	$ 92,000
Percentage of allowance of credit losses	1.19%	1.19%	1.24%
Recorded total loans	$ 9,667,375	$ 9,667,375	$ 8,150,147
Loans purchased with credit deterioration			0
Allowance for credit losses on loans purchased	17	17	3,200
Salisbury Bank [Member]
Allowance for Credit Losses [Abstract]
Loans purchased with credit deterioration	219,500	219,500
Allowance for credit losses on loans purchased	5,800	5,800
Allowance for credit losses at acquisition	14,500
Acquisition-related provision for credit losses	8,800	8,800
Salisbury Bank [Member] | PCD [Member]
Allowance for Credit Losses [Abstract]
Allowance for credit losses at acquisition	5,800
Salisbury Bank [Member] | Non-PCD [Member]
Allowance for Credit Losses [Abstract]
Allowance for credit losses at acquisition	8,800
ASU 2022-02 [Member]
Allowance for Credit Losses [Abstract]
Allowance for credit losses	114,601	114,601	100,152
Loans [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | ASU 2022-02 [Member]
Allowance for Credit Losses [Abstract]
Allowance for credit losses			(600)
Accrued Interest Receivable [Member]
Allowance for Credit Losses [Abstract]
Allowance for credit losses	0	0	0
AIR on loans	$ 32,500	$ 32,500	$ 25,000
Financing Receivable, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Other Assets	Other Assets	Other Assets
PPP [Member] | Maximum [Member]
Allowance for Credit Losses [Abstract]
Recorded total loans					$ 1,000
Residential [Member]
Allowance for Credit Losses [Abstract]
Allowance for credit losses	$ 20,607	$ 20,607		15,554		15,534	16,302	18,806
Recorded total loans	2,611,692	2,611,692	$ 2,114,495
Amount of loans purchased		$ 2,400	$ 11,500
Premium on loans purchased		7.01%	1.53%
Residential [Member] | ASU 2022-02 [Member]
Allowance for Credit Losses [Abstract]
Allowance for credit losses	20,607	$ 20,607	$ 14,539
Consumer Loans [Member]
Allowance for Credit Losses [Abstract]
Allowance for credit losses	47,274	47,274		$ 47,883		$ 48,310	$ 44,940	$ 44,253
Recorded total loans	2,195,382	2,195,382	2,099,087
Amount of loans purchased			50,100
Consumer Loans [Member] | ASU 2022-02 [Member]
Allowance for Credit Losses [Abstract]
Allowance for credit losses	$ 47,274	$ 47,274	$ 50,951