Loans and Allowance for Credit Losses - Summary of Changes in Allowance for Loan Losses by Loan Category (Details) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
Jan. 01, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 97,787	$ 147,955	$ 125,531	$ 142,211	$ 97,787
Charge-offs		(1,045)	(983)	(2,801)	(3,689)
Recoveries		908	635	2,025	3,434
Provision (release)		7,328	6,480	14,854	7,045
Ending balance		155,146	131,663	155,146	131,663
Allowance for loan losses		155,146	131,663	155,146	131,663
Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	27,086			(1,143)	27,086
Allowance for loan losses
Cumulative effect accounting adjustment \| Accounting Standards Update 2022-02
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance				(1,100)
Allowance for loan losses
Cumulative effect accounting adjustment \| Accounting Standards Update 2016-13
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	27,100				27,100
Allowance for loan losses
PCI loan balances to PCD and the associated gross-up	100
Commercial and industrial \| Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	18,018	29,535	25,852	26,859	18,018
Charge-offs		(11)	(11)	(11)	(13)
Recoveries		120	126	285	1,074
Provision (release)		(3,126)	874	(662)	(3,771)
Ending balance		26,518	26,841	26,518	26,841
Allowance for loan losses		26,518	26,841	26,518	26,841
Commercial and industrial \| Commercial Portfolio Segment \| Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	11,533			47	11,533
Allowance for loan losses
Commercial real estate \| Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	52,373	59,524	47,555	54,730	52,373
Charge-offs		0	0	0	0
Recoveries		2	3	8	53
Provision (release)		11,097	3,545	15,885	5,332
Ending balance		70,623	51,103	70,623	51,103
Allowance for loan losses		70,623	51,103	70,623	51,103
Commercial real estate \| Commercial Portfolio Segment \| Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	(6,655)			0	(6,655)
Allowance for loan losses
Commercial construction \| Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	2,585	7,663	5,474	7,085	2,585
Charge-offs		0	0	0	0
Recoveries		0	0	0	0
Provision (release)		136	507	714	1,911
Ending balance		7,799	5,981	7,799	5,981
Allowance for loan losses		7,799	5,981	7,799	5,981
Commercial construction \| Commercial Portfolio Segment \| Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,485			0	1,485
Allowance for loan losses
Business banking \| Commercial Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	10,983	15,228	16,699	16,189	10,983
Charge-offs		(303)	(369)	(900)	(1,922)
Recoveries		609	286	1,294	1,678
Provision (release)		(316)	(354)	(1,225)	(637)
Ending balance		15,218	16,262	15,218	16,262
Allowance for loan losses		15,218	16,262	15,218	16,262
Business banking \| Commercial Portfolio Segment \| Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	6,160			(140)	6,160
Allowance for loan losses
Residential real estate \| Residential Real Estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	6,556	27,012	21,663	28,129	6,556
Charge-offs		0	0	0	0
Recoveries		30	56	63	80
Provision (release)		(687)	1,288	(988)	2,882
Ending balance		26,355	23,007	26,355	23,007
Allowance for loan losses		26,355	23,007	26,355	23,007
Residential real estate \| Residential Real Estate \| Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	13,489			(849)	13,489
Allowance for loan losses
Consumer home equity \| Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,722	6,044	5,662	6,454	3,722
Charge-offs		0	0	(7)	0
Recoveries		39	6	40	16
Provision (release)		(601)	174	(804)	247
Ending balance		5,482	5,842	5,482	5,842
Allowance for loan losses		5,482	5,842	5,482	5,842
Consumer home equity \| Consumer Portfolio Segment \| Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,857			(201)	1,857
Allowance for loan losses
Other Consumer \| Consumer Portfolio Segment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	3,308	2,949	2,626	2,765	3,308
Charge-offs		(731)	(603)	(1,883)	(1,754)
Recoveries		108	158	335	533
Provision (release)		825	446	1,934	1,081
Ending balance		3,151	2,627	3,151	2,627
Allowance for loan losses		$ 3,151	2,627	3,151	2,627
Other Consumer \| Consumer Portfolio Segment \| Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	(541)			$ 0	(541)
Allowance for loan losses
Other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	242				242
Charge-offs					0
Recoveries					0
Provision (release)					0
Ending balance			0		0
Allowance for loan losses			$ 0		0
Other \| Cumulative effect accounting adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ (242)				$ (242)
Allowance for loan losses

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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479344/326-20-45-1

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossExcludingAccruedInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossRecovery
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestAllowanceForCreditLossWriteoff
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestCreditLossExpenseReversal
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, excluding accrued interest, of allowance for credit loss at acquisition date of financing receivable purchased with credit deterioration. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 19
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-19

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-13

+ Details

Name:	us-gaap_FinancingReceivableExcludingAccruedInterestPurchasedWithCreditDeteriorationAllowanceForCreditLossAtAcquisitionDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	srt_CumulativeEffectPeriodOfAdoptionAxis=srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate202202Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201613Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialAndIndustrialSectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ebc_BusinessBankingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ebc_OtherConsumerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ebc_OtherClassOfFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: