Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

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Amortized cost, before allowance for credit loss, fee, and loan in process, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

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Amount of unamortized loan commitment, origination, and other costs (fees) and purchase premium (discount) on financing receivable recognized as adjustment to yield. Excludes financing receivable covered under loss sharing agreement.

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Loans and Allowance for Credit Losses - Summary of Company's Loan Portfolio as of the Dates Indicated (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	$ 12,903,954		$ 12,281,510
Less: allowance for loan losses	(131,663)	$ (125,531)	(97,787)	$ (103,398)	$ (105,637)	$ (113,031)
Unamortized premiums, net of unearned discounts and deferred fees	(19,349)		(26,442)
Loans after the allowance for loan losses, unamortized premiums, unearned discounts and deferred fees	12,752,942		12,157,281
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Less: allowance for loan losses	(26,841)	(25,852)
Commercial and industrial \| Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	3,023,729		2,960,527
Less: allowance for loan losses	(26,841)		(18,018)	(20,629)	(22,596)	(26,617)
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Less: allowance for loan losses	(51,103)	(47,555)
Commercial real estate \| Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	4,985,654		4,522,513
Less: allowance for loan losses	(51,103)		(52,373)	(54,186)	(52,759)	(54,569)
Commercial construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Less: allowance for loan losses	(5,981)	(5,474)
Commercial construction \| Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	314,193		222,328
Less: allowance for loan losses	(5,981)		(2,585)	(3,402)	(3,446)	(4,553)
Business banking
Financing Receivable, Allowance for Credit Loss [Line Items]
Less: allowance for loan losses	(16,262)	(16,699)
Business banking \| Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,096,436		1,334,694
Less: allowance for loan losses	(16,262)		(10,983)	(11,378)	(12,705)	(13,152)
Residential real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Less: allowance for loan losses	(23,007)	(21,663)
Residential real estate \| Residential Real Estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	2,118,852		1,926,810
Less: allowance for loan losses	(23,007)		(6,556)	(6,430)	(6,478)	(6,435)
Consumer home equity
Financing Receivable, Allowance for Credit Loss [Line Items]
Less: allowance for loan losses	(5,842)	(5,662)
Consumer home equity \| Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,168,476		1,100,153
Less: allowance for loan losses	(5,842)		(3,722)	(3,635)	(3,588)	(3,744)
Other Consumer
Financing Receivable, Allowance for Credit Loss [Line Items]
Less: allowance for loan losses	(2,627)	$ (2,626)
Other Consumer \| Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	196,614		214,485
Less: allowance for loan losses	(2,627)		(3,308)	$ (3,387)	$ (3,626)	$ (3,467)
Automobile Loan \| Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	$ 24,000		$ 53,300