Loans and Allowance for Loan Losses - Summary of Information Regarding Interest Income Recognized on Impaired Loans,by Portfolio (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2021
Average Recorded Investment
With no related allowance recorded:	$ 33,874	$ 34,399
With an allowance recorded:	34,915	38,027
Total	68,789	72,426
Total Interest Recognized
With no related allowance recorded:	235	730
With an allowance recorded:	156	483
Total	391	1,213
Commercial Portfolio Segment \| Commercial and industrial
Average Recorded Investment
With no related allowance recorded:	12,517	11,405
With an allowance recorded:	7,808	7,849
Total Interest Recognized
With no related allowance recorded:	39	131
With an allowance recorded:	0	0
Commercial Portfolio Segment \| Commercial real estate
Average Recorded Investment
With no related allowance recorded:	3,909	4,047
With an allowance recorded:	0	271
Total Interest Recognized
With no related allowance recorded:	45	133
With an allowance recorded:	0	0
Commercial Portfolio Segment \| Business banking
Average Recorded Investment
With no related allowance recorded:	3,988	4,586
With an allowance recorded:	12,642	14,560
Total Interest Recognized
With no related allowance recorded:	25	75
With an allowance recorded:	14	43
Residential Real Estate \| Residential real estate
Average Recorded Investment
With no related allowance recorded:	11,561	12,349
With an allowance recorded:	12,290	13,093
Total Interest Recognized
With no related allowance recorded:	113	344
With an allowance recorded:	127	387
Consumer Portfolio Segment \| Consumer home equity
Average Recorded Investment
With no related allowance recorded:	1,877	1,988
With an allowance recorded:	2,108	2,232
Total Interest Recognized
With no related allowance recorded:	13	47
With an allowance recorded:	15	53
Consumer Portfolio Segment \| Other Consumer
Average Recorded Investment
With no related allowance recorded:	22	24
With an allowance recorded:	67	22
Total Interest Recognized
With no related allowance recorded:	0	0
With an allowance recorded:	$ 0	$ 0

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5258-111524

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 10
-Section 50
-Paragraph 17
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5258-111524

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-Subparagraph (c)(1)
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5212-111524

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