Loans and Allowance for Credit Losses - Summary of Internal Risk-rating Categories (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
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	$ 1,013,255		$ 1,013,255		$ 3,481,250
2022	3,295,162		3,295,162		2,447,552
2021	2,377,173		2,377,173		1,630,538
2020	1,520,799		1,520,799		1,094,274
2019	995,761		995,761		779,687
Prior	3,037,990		3,037,990		2,496,108
Revolving Loans	1,691,927		1,691,927		1,614,995
Revolving Loans Converted to Term Loans	14,609		14,609		18,124
Total	13,946,676		13,946,676		13,562,528
Current period gross charge-offs
Total	845	$ 1,099	1,756	$ 2,706
Commercial and industrial
Current period gross charge-offs
Total	0
Commercial and industrial | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	443,306		443,306		780,736
2022	649,317		649,317		490,827
2021	462,742		462,742		425,901
2020	373,512		373,512		204,752
2019	162,771		162,771		103,461
Prior	676,185		676,185		647,702
Revolving Loans	554,594		554,594		478,083
Revolving Loans Converted to Term Loans	3,534		3,534		1,066
Total	3,325,961		3,325,961		3,132,528
Current period gross charge-offs
2023			0
2022			0
2021			0
2020			0
2019			0
Prior			0
Revolving Loans			0
Revolving Loans Converted to Term Loans			0
Total		1	0	2
Commercial and industrial | Pass | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	443,306		443,306		778,144
2022	630,894		630,894		479,317
2021	447,036		447,036		415,990
2020	358,942		358,942		199,865
2019	162,734		162,734		100,716
Prior	672,756		672,756		639,825
Revolving Loans	549,008		549,008		473,148
Revolving Loans Converted to Term Loans	3,534		3,534		50
Total	3,268,210		3,268,210		3,087,055
Commercial and industrial | Special Mention | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		2,298
2022	10,090		10,090		1,307
2021	0		0		7,267
2020	14,131		14,131		4,841
2019	0		0		147
Prior	655		655		0
Revolving Loans	852		852		1,196
Revolving Loans Converted to Term Loans	0		0		670
Total	25,728		25,728		17,726
Commercial and industrial | Substandard | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		294
2022	8,333		8,333		4,954
2021	15,706		15,706		2,644
2020	439		439		46
2019	37		37		2,598
Prior	2,766		2,766		7,854
Revolving Loans	4,734		4,734		485
Revolving Loans Converted to Term Loans	0		0		346
Total	32,015		32,015		19,221
Commercial and industrial | Doubtful | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		5,249
2021	0		0		0
2020	0		0		0
2019	0		0		0
Prior	8		8		23
Revolving Loans	0		0		3,254
Revolving Loans Converted to Term Loans	0		0		0
Total	8		8		8,526
Commercial and industrial | Loss | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		0
2020	0		0		0
2019	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	0		0		0
Commercial real estate
Current period gross charge-offs
Total	0
Commercial real estate | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	255,484		255,484		1,510,675
2022	1,449,542		1,449,542		825,620
2021	833,793		833,793		589,959
2020	591,325		591,325		605,840
2019	571,015		571,015		501,194
Prior	1,469,009		1,469,009		1,053,298
Revolving Loans	65,701		65,701		60,590
Revolving Loans Converted to Term Loans	2,603		2,603		4,187
Total	5,238,472		5,238,472		5,151,363
Current period gross charge-offs
2023			0
2022			0
2021			0
2020			0
2019			0
Prior			0
Revolving Loans			0
Revolving Loans Converted to Term Loans			0
Total		0	0	0
Commercial real estate | Pass | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	255,484		255,484		1,510,675
2022	1,449,542		1,449,542		825,620
2021	814,467		814,467		586,567
2020	585,707		585,707		581,840
2019	538,764		538,764		461,296
Prior	1,390,561		1,390,561		1,006,160
Revolving Loans	57,492		57,492		52,590
Revolving Loans Converted to Term Loans	2,603		2,603		4,187
Total	5,094,620		5,094,620		5,028,935
Commercial real estate | Special Mention | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		771
2020	752		752		4,204
2019	0		0		15,366
Prior	15,560		15,560		12,255
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	16,312		16,312		32,596
Commercial real estate | Substandard | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	19,326		19,326		2,621
2020	4,866		4,866		19,796
2019	32,251		32,251		24,532
Prior	62,888		62,888		34,883
Revolving Loans	8,209		8,209		8,000
Revolving Loans Converted to Term Loans	0		0		0
Total	127,540		127,540		89,832
Commercial real estate | Doubtful | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		0
2020	0		0		0
2019	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	0		0		0
Commercial real estate | Loss | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		0
2020	0		0		0
2019	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	0		0		0
Commercial construction
Current period gross charge-offs
Total	0
Commercial construction | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	46,221		46,221		91,397
2022	139,127		139,127		178,648
2021	160,158		160,158		31,317
2020	11		11		20,767
2019	14,615		14,615		0
Prior	0		0		0
Revolving Loans	8,998		8,998		12,130
Revolving Loans Converted to Term Loans	0		0		0
Total	369,130		369,130		334,259
Current period gross charge-offs
2023			0
2022			0
2021			0
2020			0
2019			0
Prior			0
Revolving Loans			0
Revolving Loans Converted to Term Loans			0
Total		0	0	0
Commercial construction | Pass | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	42,767		42,767		91,397
2022	139,127		139,127		178,648
2021	160,158		160,158		28,956
2020	0		0		20,767
2019	14,615		14,615		0
Prior	0		0		0
Revolving Loans	8,998		8,998		12,130
Revolving Loans Converted to Term Loans	0		0		0
Total	365,665		365,665		331,898
Commercial construction | Special Mention | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	3,454		3,454		0
2022	0		0		0
2021	0		0		2,361
2020	11		11		0
2019	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	3,465		3,465		2,361
Commercial construction | Substandard | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		0
2020	0		0		0
2019	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	0		0		0
Commercial construction | Doubtful | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		0
2020	0		0		0
2019	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	0		0		0
Commercial construction | Loss | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		0
2020	0		0		0
2019	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	0		0		0
Business banking
Current period gross charge-offs
Total	254
Business banking | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	70,449		70,449		178,806
2022	168,687		168,687		206,703
2021	196,838		196,838		176,147
2020	164,420		164,420		135,731
2019	130,539		130,539		63,762
Prior	282,604		282,604		248,643
Revolving Loans	77,503		77,503		80,455
Revolving Loans Converted to Term Loans	3,044		3,044		4,991
Total	1,094,084		1,094,084		1,095,238
Current period gross charge-offs
2023			0
2022			54
2021			51
2020			33
2019			68
Prior			259
Revolving Loans			0
Revolving Loans Converted to Term Loans			132
Total		608	597	1,553
Business banking | Pass | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	69,045		69,045		178,806
2022	168,161		168,161		202,230
2021	192,236		192,236		170,088
2020	159,445		159,445		128,282
2019	124,249		124,249		59,452
Prior	267,125		267,125		233,484
Revolving Loans	76,124		76,124		78,080
Revolving Loans Converted to Term Loans	2,993		2,993		4,770
Total	1,059,378		1,059,378		1,055,192
Business banking | Special Mention | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	526		526		991
2021	977		977		4,635
2020	2,771		2,771		4,605
2019	4,090		4,090		3,740
Prior	9,845		9,845		7,584
Revolving Loans	68		68		145
Revolving Loans Converted to Term Loans	27		27		0
Total	18,304		18,304		21,700
Business banking | Substandard | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	1,404		1,404		0
2022	0		0		3,482
2021	3,625		3,625		1,424
2020	2,183		2,183		2,663
2019	1,097		1,097		570
Prior	5,115		5,115		7,505
Revolving Loans	1,311		1,311		2,230
Revolving Loans Converted to Term Loans	24		24		221
Total	14,759		14,759		18,095
Business banking | Doubtful | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		0
2020	21		21		181
2019	1,103		1,103		0
Prior	519		519		70
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	1,643		1,643		251
Business banking | Loss | Commercial Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		0
2020	0		0		0
2019	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	0		0		0
Residential real estate
Current period gross charge-offs
Total	0
Residential real estate | Residential Real Estate
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	123,231		123,231		766,094
2022	756,265		756,265		702,429
2021	685,561		685,561		383,651
2020	371,207		371,207		103,747
2019	97,566		97,566		70,668
Prior	495,389		495,389		453,466
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	2,529,219		2,529,219		2,480,055
Current period gross charge-offs
2023			0
2022			0
2021			0
2020			0
2019			0
Prior			0
Revolving Loans			0
Revolving Loans Converted to Term Loans			0
Total		0	0	0
Residential real estate | Residential Real Estate | Current and accruing
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	122,270		122,270		761,442
2022	746,261		746,261		696,959
2021	675,190		675,190		382,262
2020	369,323		369,323		99,494
2019	95,281		95,281		66,702
Prior	476,481		476,481		434,720
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	2,484,806		2,484,806		2,441,579
Residential real estate | Residential Real Estate | 30-89 days past due and accruing
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	961		961		4,652
2022	9,534		9,534		5,470
2021	10,087		10,087		1,245
2020	1,884		1,884		2,762
2019	1,996		1,996		2,951
Prior	11,155		11,155		11,646
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	35,617		35,617		28,726
Residential real estate | Residential Real Estate | Loans 90 days or more past due and still accruing
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		0
2020	0		0		0
2019	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	0		0		0
Residential real estate | Residential Real Estate | Non-accrual
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	470		470		0
2021	284		284		144
2020	0		0		1,491
2019	289		289		1,015
Prior	7,753		7,753		7,100
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	8,796		8,796		9,750
Consumer home equity
Current period gross charge-offs
Total	0
Consumer home equity | Consumer Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	21,721		21,721		97,954
2022	90,110		90,110		10,774
2021	9,894		9,894		5,840
2020	5,426		5,426		5,076
2019	4,606		4,606		21,438
Prior	92,524		92,524		76,174
Revolving Loans	971,988		971,988		966,188
Revolving Loans Converted to Term Loans	5,355		5,355		7,863
Total	1,201,624		1,201,624		1,191,307
Current period gross charge-offs
2023			0
2022			0
2021			0
2020			0
2019			0
Prior			0
Revolving Loans			7
Revolving Loans Converted to Term Loans			0
Total		0	7	0
Consumer home equity | Consumer Portfolio Segment | Current and accruing
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	21,721		21,721		97,395
2022	89,846		89,846		10,774
2021	9,894		9,894		5,840
2020	5,426		5,426		5,015
2019	4,606		4,606		21,092
Prior	89,534		89,534		73,927
Revolving Loans	959,311		959,311		953,829
Revolving Loans Converted to Term Loans	5,238		5,238		7,320
Total	1,185,576		1,185,576		1,175,192
Consumer home equity | Consumer Portfolio Segment | 30-89 days past due and accruing
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		559
2022	264		264		0
2021	0		0		0
2020	0		0		0
2019	0		0		72
Prior	926		926		944
Revolving Loans	7,428		7,428		7,239
Revolving Loans Converted to Term Loans	69		69		247
Total	8,687		8,687		9,061
Consumer home equity | Consumer Portfolio Segment | Loans 90 days or more past due and still accruing
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		0
2020	0		0		0
2019	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	0		0		0
Consumer home equity | Consumer Portfolio Segment | Non-accrual
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		0
2020	0		0		61
2019	0		0		274
Prior	2,064		2,064		1,303
Revolving Loans	5,249		5,249		5,120
Revolving Loans Converted to Term Loans	48		48		296
Total	7,361		7,361		7,054
Other Consumer
Current period gross charge-offs
Total	591
Other Consumer | Consumer Portfolio Segment
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	52,843		52,843		55,588
2022	42,114		42,114		32,551
2021	28,187		28,187		17,723
2020	14,898		14,898		18,361
2019	14,649		14,649		19,164
Prior	22,279		22,279		16,825
Revolving Loans	13,143		13,143		17,549
Revolving Loans Converted to Term Loans	73		73		17
Total	188,186		188,186		177,778
Current period gross charge-offs
2023			461
2022			177
2021			163
2020			76
2019			54
Prior			138
Revolving Loans			83
Revolving Loans Converted to Term Loans			0
Total		$ 490	1,152	$ 1,151
Other Consumer | Consumer Portfolio Segment | Current and accruing
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	52,817		52,817		55,414
2022	41,880		41,880		32,390
2021	28,008		28,008		17,641
2020	14,871		14,871		18,298
2019	14,592		14,592		18,832
Prior	21,877		21,877		16,603
Revolving Loans	12,994		12,994		17,476
Revolving Loans Converted to Term Loans	73		73		0
Total	187,112		187,112		176,654
Other Consumer | Consumer Portfolio Segment | 30-89 days past due and accruing
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	26		26		143
2022	155		155		68
2021	121		121		43
2020	22		22		61
2019	41		41		240
Prior	355		355		178
Revolving Loans	131		131		58
Revolving Loans Converted to Term Loans	0		0		7
Total	851		851		798
Other Consumer | Consumer Portfolio Segment | Loans 90 days or more past due and still accruing
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		0
2022	0		0		0
2021	0		0		0
2020	0		0		0
2019	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans Converted to Term Loans	0		0		0
Total	0		0		0
Other Consumer | Consumer Portfolio Segment | Non-accrual
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
2023	0		0		31
2022	79		79		93
2021	58		58		39
2020	5		5		2
2019	16		16		92
Prior	47		47		44
Revolving Loans	18		18		15
Revolving Loans Converted to Term Loans	0		0		10
Total	$ 223		$ 223		$ 326