Loans and Allowance for Credit Losses - Summary of Changes in Allowance for Loan Losses by Loan Category (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 01, 2022	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 97,787	$ 140,938	$ 124,166	$ 142,211	$ 97,787
Charge-offs		(845)	(1,099)	(1,756)	(2,706)
Recoveries		361	1,414	1,117	2,799
Provision (release)		7,501	1,050	7,526	565
Ending balance		147,955	125,531	147,955	125,531
Allowance for loan losses		147,955	125,531	147,955	125,531
Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	27,086			(1,143)	27,086
Allowance for loan losses
Cumulative effect accounting adjustment | Accounting Standards Update 2022-02
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance				(1,100)
Allowance for loan losses
Cumulative effect accounting adjustment | Accounting Standards Update 2016-13
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	27,100				27,100
Allowance for loan losses
Financing receivable, excluding accrued interest, purchased with credit deterioration, allowance for credit loss at acquisition date	100
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		26,929
Charge-offs		0
Recoveries		26
Provision (release)		2,580
Ending balance		29,535		29,535
Allowance for loan losses		29,535		29,535
Commercial and industrial | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	18,018		26,841	26,859	18,018
Charge-offs			(1)	0	(2)
Recoveries			698	165	948
Provision (release)			(1,686)	2,464	(4,645)
Ending balance		29,535	25,852	29,535	25,852
Allowance for loan losses		29,535	25,852	29,535	25,852
Commercial and industrial | Commercial Portfolio Segment | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	11,533			47	11,533
Allowance for loan losses
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		55,193
Charge-offs		0
Recoveries		2
Provision (release)		4,329
Ending balance		59,524		59,524
Allowance for loan losses		59,524		59,524
Commercial real estate | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	52,373		44,612	54,730	52,373
Charge-offs			0	0	0
Recoveries			36	6	50
Provision (release)			2,907	4,788	1,787
Ending balance		59,524	47,555	59,524	47,555
Allowance for loan losses		59,524	47,555	59,524	47,555
Commercial real estate | Commercial Portfolio Segment | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	(6,655)			0	(6,655)
Allowance for loan losses
Commercial construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		7,578
Charge-offs		0
Recoveries		0
Provision (release)		85
Ending balance		7,663		7,663
Allowance for loan losses		7,663		7,663
Commercial construction | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	2,585		4,414	7,085	2,585
Charge-offs			0	0	0
Recoveries			0	0	0
Provision (release)			1,060	578	1,404
Ending balance		7,663	5,474	7,663	5,474
Allowance for loan losses		7,663	5,474	7,663	5,474
Commercial construction | Commercial Portfolio Segment | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,485			0	1,485
Allowance for loan losses
Business banking
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		15,085
Charge-offs		(254)
Recoveries		204
Provision (release)		193
Ending balance		15,228		15,228
Allowance for loan losses		15,228		15,228
Business banking | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	10,983		17,269	16,189	10,983
Charge-offs			(608)	(597)	(1,553)
Recoveries			464	685	1,392
Provision (release)			(426)	(909)	(283)
Ending balance		15,228	16,699	15,228	16,699
Allowance for loan losses		15,228	16,699	15,228	16,699
Business banking | Commercial Portfolio Segment | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	6,160			(140)	6,160
Allowance for loan losses
Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		27,130
Charge-offs		0
Recoveries		18
Provision (release)		(136)
Ending balance		27,012		27,012
Allowance for loan losses		27,012		27,012
Residential real estate | Residential Real Estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	6,556		22,243	28,129	6,556
Charge-offs			0	0	0
Recoveries			14	33	24
Provision (release)			(594)	(301)	1,594
Ending balance		27,012	21,663	27,012	21,663
Allowance for loan losses		27,012	21,663	27,012	21,663
Residential real estate | Residential Real Estate | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	13,489			(849)	13,489
Allowance for loan losses
Consumer home equity
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		6,182
Charge-offs		0
Recoveries		0
Provision (release)		(138)
Ending balance		6,044		6,044
Allowance for loan losses		6,044		6,044
Consumer home equity | Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,722		6,018	6,454	3,722
Charge-offs			0	(7)	0
Recoveries			6	1	10
Provision (release)			(362)	(203)	73
Ending balance		6,044	5,662	6,044	5,662
Allowance for loan losses		6,044	5,662	6,044	5,662
Consumer home equity | Consumer Portfolio Segment | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,857			(201)	1,857
Allowance for loan losses
Other Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		2,841
Charge-offs		(591)
Recoveries		111
Provision (release)		588
Ending balance		2,949		2,949
Allowance for loan losses		2,949		2,949
Other Consumer | Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,308		2,769	2,765	3,308
Charge-offs			(490)	(1,152)	(1,151)
Recoveries			196	227	375
Provision (release)			151	1,109	635
Ending balance		2,949	2,626	2,949	2,626
Allowance for loan losses		$ 2,949	2,626	2,949	2,626
Other Consumer | Consumer Portfolio Segment | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	(541)			$ 0	(541)
Allowance for loan losses
Other Class Of Financing Receivable [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	242				242
Charge-offs					0
Recoveries					0
Provision (release)					0
Ending balance			0		0
Allowance for loan losses			$ 0		0
Other Class Of Financing Receivable [Member] | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ (242)				$ (242)
Allowance for loan losses