Loans and Allowance for Loan Losses - Summary of the Company's Loan participations (Detail) - Loan Participations and Assignments - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Mar. 31, 2021	Jun. 30, 2020	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance	$ 1,011,551		$ 1,024,709
Nonperforming Loan Rate (%)	0.75%		0.65%
Impaired (%)	0.75%		0.65%
Gross Charge-offs	$ 0	$ 0
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance	$ 579,812		$ 598,873
Nonperforming Loan Rate (%)	1.31%		1.11%
Impaired (%)	1.31%		1.11%
Gross Charge-offs	$ 0	0
Commercial real estate
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance	$ 345,261		$ 306,202
Nonperforming Loan Rate (%)	0.00%		0.00%
Impaired (%)	0.00%		0.00%
Gross Charge-offs	$ 0	0
Commercial construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance	$ 86,447		$ 119,600
Nonperforming Loan Rate (%)	0.00%		0.00%
Impaired (%)	0.00%		0.00%
Gross Charge-offs	$ 0	0
Business banking
Financing Receivable, Allowance for Credit Loss [Line Items]
Balance	$ 31		$ 34
Nonperforming Loan Rate (%)	0.00%		0.00%
Impaired (%)	0.00%		0.00%
Gross Charge-offs	$ 0	$ 0

Non performing loan percentage.

No definition available.

Name:	ebc_NonPerformingLoanPercentage
Namespace Prefix:	ebc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Net credit losses are charge-offs and are based on total loans outstanding during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (e)(5)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Cost of the investment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=99383244&loc=d3e12121-115841

+ Details

Name:	us-gaap_InvestmentOwnedAtCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Reflects the percentage derived from dividing impaired loans on which interest has ceased to be accrued by total loans.

+ References

No definition available.

+ Details

Name:	us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_LoanParticipationsAndAssignmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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