Credit exposure to settled variation margin in excess of customer related interest rate swap.

No definition available.

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Namespace Prefix:	ebc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624258-113959

+ Details

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

- Definition

Fair value of credit risk derivative asset after deduction of credit risk derivative liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4K
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5708775-113959

+ Details

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

- 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

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

- Definition

The estimated net amount of unrealized gains or losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121549185&loc=d3e80748-113994

+ Details

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

- Details

Name:	ebc_NatureOfTransactionAxis=ebc_NonClearedDerivativeTransactionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditDerivativesByContractTypeAxis=ebc_CustomerRelatedInterestRateSwapDerivativesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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Balance Type:
Period Type:

- Details

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- Details

Name:	ebc_NatureOfTransactionAxis=ebc_ClearedDerivativeTransactionMember
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Data Type:	na
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- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_InterestIncomeMember
Namespace Prefix:
Data Type:	na
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Period Type:

- Details

Name:	ebc_EventAxis=ebc_TerminationOfCashFlowHedgesMember
Namespace Prefix:
Data Type:	na
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Period Type:

Derivative Financial Instruments - Additional information (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Credit exposure to settled variation margin in excess of customer related interest rate swap	$ 0.5	$ 0.1
Non Cleared Derivative Transactions \| Customer Related Interest Rate Swap Derivatives
Derivative [Line Items]
Fair value of interest rate swap liabilities that are net in a net liability position	26.1	42.6
Cash and Cash Equivalents \| Non Cleared Derivative Transactions \| Customer Related Interest Rate Swap Derivatives
Derivative [Line Items]
Additional collateral posted	35.0
Available-for-sale Securities \| Non Cleared Derivative Transactions \| Customer Related Interest Rate Swap Derivatives
Derivative [Line Items]
Additional collateral posted		49.2
Restricted Assets \| Cash and Cash Equivalents \| Cleared Derivative Transaction
Derivative [Line Items]
Additional collateral posted	49.5
Restricted Assets \| Available-for-sale Securities \| Cleared Derivative Transaction
Derivative [Line Items]
Additional collateral posted		$ 60.4
Interest Income \| Termination Of Cash Flow Hedges
Derivative [Line Items]
Interest rate swap cash flow hedges amount expected to reclassified from other comprehensive income to income statement in the next twelve months	$ 23.1