Loans and Allowance for Loan Losses - Summary of Company's Loan Portfolio as of the Dates Indicated (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	$ 12,182,203	$ 12,281,510
Less: allowance for loan losses	(124,166)	(97,787)	$ (111,080)	$ (113,031)
Unamortized premiums, net of unearned discounts and deferred fees	(24,434)	(26,442)
Loans after the allowance for loan losses, unamortized premiums, unearned discounts and deferred fees	12,033,603	12,157,281
Commercial and industrial \| Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	2,886,560	2,960,527
Less: allowance for loan losses	(26,841)	(18,018)	(25,406)	(26,617)
Commercial real estate \| Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	4,609,824	4,522,513
Less: allowance for loan losses	(44,612)	(52,373)	(55,138)	(54,569)
Commercial construction \| Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	246,093	222,328
Less: allowance for loan losses	(4,414)	(2,585)	(3,350)	(4,553)
Business Banking \| Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,201,007	1,334,694
Less: allowance for loan losses	(17,269)	(10,983)	(13,504)	(13,152)
Residential real estate \| Residential Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,936,182	1,926,810
Less: allowance for loan losses	(22,243)	(6,556)	(6,235)	(6,435)
Consumer home equity \| Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	1,099,211	1,100,153
Less: allowance for loan losses	(6,018)	(3,722)	(3,576)	(3,744)
Other Consumer \| Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Line Items]
Gross loans before unamortized premiums, unearned discounts and deferred fees	203,326	214,485
Less: allowance for loan losses	$ (2,769)	$ (3,308)	$ (3,498)	$ (3,467)

Amount excluding accrued interest, of allowance for credit loss on financing receivable.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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