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		12 Months Ended
	Jan. 01, 2022	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 97,787	$ 124,166	$ 111,080	$ 97,787	$ 113,031	$ 113,031
Charge-offs		(1,099)	(2,663)	(2,706)	(4,645)
Recoveries		1,414	520	2,799	1,131
Provision for (release of) allowance for loan losses		1,050	(3,300)	565	(3,880)
Ending balance		125,531	105,637	125,531	105,637	97,787
Allowance for loan losses		125,531	105,637	125,531	105,637	97,787
Financing receivable, excluding accrued interest, purchased with credit deterioration, allowance for credit loss at acquisition date						93,271
Financing receivable, accrued interest, before allowance for credit loss		32,800		32,800
Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	27,086			27,086
Ending balance						27,086
Allowance for loan losses						27,086
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		26,841
Charge-offs		(1)
Recoveries		698
Provision for (release of) allowance for loan losses		(1,686)
Ending balance		25,852		25,852
Allowance for loan losses		25,852		25,852
Commercial and industrial | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	18,018		25,406	18,018	26,617	26,617
Charge-offs			(550)	(2)	(550)
Recoveries			13	948	22
Provision for (release of) allowance for loan losses			(2,273)	(4,645)	(3,493)
Ending balance		25,852	22,596	25,852	22,596	18,018
Allowance for loan losses		25,852	22,596	25,852	22,596	18,018
Financing receivable, excluding accrued interest, purchased with credit deterioration, allowance for credit loss at acquisition date						16,473
Commercial and industrial | Commercial Portfolio Segment | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	11,533			11,533
Ending balance						11,533
Allowance for loan losses						11,533
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		44,612
Charge-offs		0
Recoveries		36
Provision for (release of) allowance for loan losses		2,907
Ending balance		47,555		47,555
Allowance for loan losses		47,555		47,555
Commercial real estate | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	52,373		55,138	52,373	54,569	54,569
Charge-offs			0	0	(234)
Recoveries			4	50	4
Provision for (release of) allowance for loan losses			(2,383)	1,787	(1,580)
Ending balance		47,555	52,759	47,555	52,759	52,373
Allowance for loan losses		47,555	52,759	47,555	52,759	52,373
Financing receivable, excluding accrued interest, purchased with credit deterioration, allowance for credit loss at acquisition date						52,075
Commercial real estate | Commercial Portfolio Segment | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	(6,655)			(6,655)
Ending balance						(6,655)
Allowance for loan losses						(6,655)
Commercial construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		4,414
Charge-offs		0
Recoveries		0
Provision for (release of) allowance for loan losses		1,060
Ending balance		5,474		5,474
Allowance for loan losses		5,474		5,474
Commercial construction | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	2,585		3,350	2,585	4,553	4,553
Charge-offs			0	0	0
Recoveries			0	0	0
Provision for (release of) allowance for loan losses			96	1,404	(1,107)
Ending balance		5,474	3,446	5,474	3,446	2,585
Allowance for loan losses		5,474	3,446	5,474	3,446	2,585
Financing receivable, excluding accrued interest, purchased with credit deterioration, allowance for credit loss at acquisition date						2,585
Commercial construction | Commercial Portfolio Segment | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,485			1,485
Ending balance						1,485
Allowance for loan losses						1,485
Business banking
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		17,269
Charge-offs		(608)
Recoveries		464
Provision for (release of) allowance for loan losses		(426)
Ending balance		16,699		16,699
Allowance for loan losses		16,699		16,699
Business banking | Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	10,983		13,504	10,983	13,152	13,152
Charge-offs			(1,838)	(1,553)	(3,222)
Recoveries			291	1,392	656
Provision for (release of) allowance for loan losses			748	(283)	2,119
Ending balance		16,699	12,705	16,699	12,705	10,983
Allowance for loan losses		16,699	12,705	16,699	12,705	10,983
Financing receivable, excluding accrued interest, purchased with credit deterioration, allowance for credit loss at acquisition date						10,533
Business banking | Commercial Portfolio Segment | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	6,160			6,160
Ending balance						6,160
Allowance for loan losses						6,160
Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		22,243
Charge-offs		0
Recoveries		14
Provision for (release of) allowance for loan losses		(594)
Ending balance		21,663		21,663
Allowance for loan losses		21,663		21,663
Residential real estate | Residential Real Estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	6,556		6,235	6,556	6,435	6,435
Charge-offs			0	0	0
Recoveries			17	24	27
Provision for (release of) allowance for loan losses			226	1,594	16
Ending balance		21,663	6,478	21,663	6,478	6,556
Allowance for loan losses		21,663	6,478	21,663	6,478	6,556
Financing receivable, excluding accrued interest, purchased with credit deterioration, allowance for credit loss at acquisition date						4,764
Residential real estate | Residential Real Estate | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	13,489			13,489
Ending balance						13,489
Allowance for loan losses						13,489
Consumer home equity
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		6,018
Charge-offs		0
Recoveries		6
Provision for (release of) allowance for loan losses		(362)
Ending balance		5,662		5,662
Allowance for loan losses		5,662		5,662
Consumer home equity | Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,722		3,576	3,722	3,744	3,744
Charge-offs			0	0	0
Recoveries			3	10	74
Provision for (release of) allowance for loan losses			9	73	(230)
Ending balance		5,662	3,588	5,662	3,588	3,722
Allowance for loan losses		5,662	3,588	5,662	3,588	3,722
Financing receivable, excluding accrued interest, purchased with credit deterioration, allowance for credit loss at acquisition date						3,452
Consumer home equity | Consumer Portfolio Segment | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,857			1,857
Ending balance						1,857
Allowance for loan losses						1,857
Other Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		2,769
Charge-offs		(490)
Recoveries		196
Provision for (release of) allowance for loan losses		151
Ending balance		2,626		2,626
Allowance for loan losses		2,626		2,626
Other Consumer | Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,308		3,498	3,308	3,467	3,467
Charge-offs			(275)	(1,151)	(639)
Recoveries			192	375	348
Provision for (release of) allowance for loan losses			211	635	450
Ending balance		2,626	3,626	2,626	3,626	3,308
Allowance for loan losses		2,626	3,626	2,626	3,626	3,308
Financing receivable, excluding accrued interest, purchased with credit deterioration, allowance for credit loss at acquisition date						3,147
Other Consumer | Consumer Portfolio Segment | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	(541)			(541)
Ending balance						(541)
Allowance for loan losses						(541)
Other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	242		373	242	494	494
Charge-offs			0	0	0
Recoveries			0	0	0
Provision for (release of) allowance for loan losses			66	0	(55)
Ending balance		0	439	0	439	242
Allowance for loan losses		$ 0	$ 439	0	$ 439	242
Financing receivable, excluding accrued interest, purchased with credit deterioration, allowance for credit loss at acquisition date						242
Other | Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ (242)			$ (242)
Ending balance						(242)
Allowance for loan losses						$ (242)