Loans and Allowance for Loan Losses - Summary of Changes in Allowance for Loan Losses by Loan Category (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 125,531	$ 105,637	$ 97,787	$ 113,031	$ 113,031
Charge-offs	(983)	(1,617)	(3,689)	(6,262)
Recoveries	635	866	3,434	1,997
Provision for (release of) allowance for loan losses	6,480	(1,488)	7,045	(5,368)
Ending balance	131,663	103,398	131,663	103,398	97,787
Individually evaluated for impairment					3,970
Acquired with deteriorated credit quality					546
Collectively evaluated for impairment					93,271
Allowance for loan losses	131,663	103,398	131,663	103,398	97,787
Loans ending balance:
Individually evaluated for impairment					58,204
Acquired with deteriorated credit quality					69,639
Collectively evaluated for impairment					12,153,667
Gross loans before unamortized premiums, unearned discounts and deferred fees	12,903,954		12,903,954		12,281,510
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	25,852
Charge-offs	(11)
Recoveries	126
Provision for (release of) allowance for loan losses	874
Ending balance	26,841		26,841
Allowance for loan losses	26,841		26,841
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	47,555
Charge-offs	0
Recoveries	3
Provision for (release of) allowance for loan losses	3,545
Ending balance	51,103		51,103
Allowance for loan losses	51,103		51,103
Commercial construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	5,474
Charge-offs	0
Recoveries	0
Provision for (release of) allowance for loan losses	507
Ending balance	5,981		5,981
Allowance for loan losses	5,981		5,981
Business banking
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	16,699
Charge-offs	(369)
Recoveries	286
Provision for (release of) allowance for loan losses	(354)
Ending balance	16,262		16,262
Allowance for loan losses	16,262		16,262
Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	21,663
Charge-offs	0
Recoveries	56
Provision for (release of) allowance for loan losses	1,288
Ending balance	23,007		23,007
Allowance for loan losses	23,007		23,007
Consumer home equity
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	5,662
Charge-offs	0
Recoveries	6
Provision for (release of) allowance for loan losses	174
Ending balance	5,842		5,842
Allowance for loan losses	5,842		5,842
Other Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	2,626
Charge-offs	(603)
Recoveries	158
Provision for (release of) allowance for loan losses	446
Ending balance	2,627		2,627
Allowance for loan losses	2,627		2,627
Other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		439	242	494	494
Charge-offs		0	0	0
Recoveries		0	0	0
Provision for (release of) allowance for loan losses		(88)	0	(143)
Ending balance	0	351	0	351	242
Individually evaluated for impairment					0
Acquired with deteriorated credit quality					0
Collectively evaluated for impairment					242
Allowance for loan losses	0	351	0	351	242
Loans ending balance:
Individually evaluated for impairment					0
Acquired with deteriorated credit quality					0
Collectively evaluated for impairment					0
Gross loans before unamortized premiums, unearned discounts and deferred fees					0
Commercial Portfolio Segment | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		22,596	18,018	26,617	26,617
Charge-offs		0	(13)	(550)
Recoveries		40	1,074	62
Provision for (release of) allowance for loan losses		(2,007)	(3,771)	(5,500)
Ending balance	26,841	20,629	26,841	20,629	18,018
Individually evaluated for impairment					1,540
Acquired with deteriorated credit quality					5
Collectively evaluated for impairment					16,473
Allowance for loan losses	26,841	20,629	26,841	20,629	18,018
Loans ending balance:
Individually evaluated for impairment					16,145
Acquired with deteriorated credit quality					19,028
Collectively evaluated for impairment					2,925,354
Gross loans before unamortized premiums, unearned discounts and deferred fees	3,023,729		3,023,729		2,960,527
Commercial Portfolio Segment | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		52,759	52,373	54,569	54,569
Charge-offs		(8)	0	(242)
Recoveries		0	53	4
Provision for (release of) allowance for loan losses		1,435	5,332	(145)
Ending balance	51,103	54,186	51,103	54,186	52,373
Individually evaluated for impairment					0
Acquired with deteriorated credit quality					298
Collectively evaluated for impairment					52,075
Allowance for loan losses	51,103	54,186	51,103	54,186	52,373
Loans ending balance:
Individually evaluated for impairment					3,520
Acquired with deteriorated credit quality					47,553
Collectively evaluated for impairment					4,471,440
Gross loans before unamortized premiums, unearned discounts and deferred fees	4,985,654		4,985,654		4,522,513
Commercial Portfolio Segment | Commercial construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		3,446	2,585	4,553	4,553
Charge-offs		0	0	0
Recoveries		0	0	0
Provision for (release of) allowance for loan losses		(44)	1,911	(1,151)
Ending balance	5,981	3,402	5,981	3,402	2,585
Individually evaluated for impairment					0
Acquired with deteriorated credit quality					0
Collectively evaluated for impairment					2,585
Allowance for loan losses	5,981	3,402	5,981	3,402	2,585
Loans ending balance:
Individually evaluated for impairment					0
Acquired with deteriorated credit quality					0
Collectively evaluated for impairment					222,328
Gross loans before unamortized premiums, unearned discounts and deferred fees	314,193		314,193		222,328
Commercial Portfolio Segment | Business banking
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		12,705	10,983	13,152	13,152
Charge-offs		(867)	(1,922)	(4,089)
Recoveries		469	1,678	1,125
Provision for (release of) allowance for loan losses		(929)	(637)	1,190
Ending balance	16,262	11,378	16,262	11,378	10,983
Individually evaluated for impairment					450
Acquired with deteriorated credit quality					0
Collectively evaluated for impairment					10,533
Allowance for loan losses	16,262	11,378	16,262	11,378	10,983
Loans ending balance:
Individually evaluated for impairment					12,060
Acquired with deteriorated credit quality					0
Collectively evaluated for impairment					1,322,634
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,096,436		1,096,436		1,334,694
Residential Real Estate | Residential real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		6,478	6,556	6,435	6,435
Charge-offs		0	0	0
Recoveries		88	80	115
Provision for (release of) allowance for loan losses		(136)	2,882	(120)
Ending balance	23,007	6,430	23,007	6,430	6,556
Individually evaluated for impairment					1,549
Acquired with deteriorated credit quality					243
Collectively evaluated for impairment					4,764
Allowance for loan losses	23,007	6,430	23,007	6,430	6,556
Loans ending balance:
Individually evaluated for impairment					22,378
Acquired with deteriorated credit quality					3,058
Collectively evaluated for impairment					1,901,374
Gross loans before unamortized premiums, unearned discounts and deferred fees	2,118,852		2,118,852		1,926,810
Consumer Portfolio Segment | Consumer home equity
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		3,588	3,722	3,744	3,744
Charge-offs		0	0	0
Recoveries		63	16	137
Provision for (release of) allowance for loan losses		(16)	247	(246)
Ending balance	5,842	3,635	5,842	3,635	3,722
Individually evaluated for impairment					270
Acquired with deteriorated credit quality					0
Collectively evaluated for impairment					3,452
Allowance for loan losses	5,842	3,635	5,842	3,635	3,722
Loans ending balance:
Individually evaluated for impairment					3,922
Acquired with deteriorated credit quality					0
Collectively evaluated for impairment					1,096,231
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,168,476		1,168,476		1,100,153
Consumer Portfolio Segment | Other Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance		3,626	3,308	3,467	3,467
Charge-offs		(742)	(1,754)	(1,381)
Recoveries		206	533	554
Provision for (release of) allowance for loan losses		297	1,081	747
Ending balance	2,627	3,387	2,627	3,387	3,308
Individually evaluated for impairment					161
Acquired with deteriorated credit quality					0
Collectively evaluated for impairment					3,147
Allowance for loan losses	2,627	$ 3,387	2,627	$ 3,387	3,308
Loans ending balance:
Individually evaluated for impairment					179
Acquired with deteriorated credit quality					0
Collectively evaluated for impairment					214,306
Gross loans before unamortized premiums, unearned discounts and deferred fees	$ 196,614		$ 196,614		$ 214,485