Loans and Allowance for Credit Losses - Summary of Shows the Age Analysis of Past Due Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Financing Receivable, Past Due [Line Items]
Total Loans	$ 12,884,605	$ 12,281,510
Total loans	12,903,954	12,281,510
Financial Asset, Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Loans	45,993	79,414
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	23,443	53,510
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	5,435	7,393
90 or More Days Past Due
Financing Receivable, Past Due [Line Items]
Total Loans	17,115	18,511
Current
Financing Receivable, Past Due [Line Items]
Total Loans	12,838,612	12,202,096
Commercial and industrial | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	3,005,172	2,960,527
Total loans	3,023,729	2,960,527
Commercial and industrial | Financial Asset, Past Due [Member] | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	2,298	1,748
Commercial and industrial | 30-59 Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	0	45
Commercial and industrial | 60-89 Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	304	31
Commercial and industrial | 90 or More Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	1,994	1,672
Commercial and industrial | Current | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	3,002,874	2,958,779
Commercial real estate | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	4,982,527	4,522,513
Total loans	4,985,654	4,522,513
Commercial real estate | Financial Asset, Past Due [Member] | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	0	27,127
Commercial real estate | 30-59 Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	0	25,931
Commercial real estate | 60-89 Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Commercial real estate | 90 or More Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	0	1,196
Commercial real estate | Current | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	4,982,527	4,495,386
Commercial construction | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	312,472	222,328
Total loans	314,193	222,328
Commercial construction | Financial Asset, Past Due [Member] | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Commercial construction | 30-59 Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Commercial construction | 60-89 Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Commercial construction | 90 or More Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Commercial construction | Current | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	312,472	222,328
Business banking | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	1,101,019	1,334,694
Total loans	1,096,436	1,334,694
Business banking | Financial Asset, Past Due [Member] | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	10,388	11,476
Business banking | 30-59 Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	5,591	5,043
Business banking | 60-89 Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	1,188	1,793
Business banking | 90 or More Days Past Due | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	3,609	4,640
Business banking | Current | Commercial Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	1,090,631	1,323,218
Residential real estate | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Total Loans	2,130,697	1,926,810
Total loans	2,118,852	1,926,810
Residential real estate | Financial Asset, Past Due [Member] | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Total Loans	21,065	26,577
Residential real estate | 30-59 Days Past Due | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Total Loans	12,572	17,523
Residential real estate | 60-89 Days Past Due | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Total Loans	1,905	3,511
Residential real estate | 90 or More Days Past Due | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Total Loans	6,588	5,543
Residential real estate | Current | Residential Real Estate
Financing Receivable, Past Due [Line Items]
Total Loans	2,109,632	1,900,233
Consumer home equity | Consumer Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	1,171,991	1,100,153
Total loans	1,168,476	1,100,153
Consumer home equity | Financial Asset, Past Due [Member] | Consumer Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	10,797	9,855
Consumer home equity | 30-59 Days Past Due | Consumer Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	4,560	3,774
Consumer home equity | 60-89 Days Past Due | Consumer Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	1,752	1,510
Consumer home equity | 90 or More Days Past Due | Consumer Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	4,485	4,571
Consumer home equity | Current | Consumer Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	1,161,194	1,090,298
Other Consumer | Consumer Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	180,727	214,485
Total loans	196,614	214,485
Other Consumer | Financial Asset, Past Due [Member] | Consumer Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	1,445	2,631
Other Consumer | 30-59 Days Past Due | Consumer Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	720	1,194
Other Consumer | 60-89 Days Past Due | Consumer Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	286	548
Other Consumer | 90 or More Days Past Due | Consumer Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	439	889
Other Consumer | Current | Consumer Portfolio Segment
Financing Receivable, Past Due [Line Items]
Total Loans	$ 179,282	$ 211,854