Loans, Allowance for Credit Losses and Credit Quality Troubled Debt Restructurings (Details) $ in Thousands	3 Months Ended
Mar. 31, 2021 USD ($) contract	Mar. 31, 2020 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts \| contract	7	5
Financing Receivable, Troubled Debt Restructuring, Premodification	$ 18,212	$ 1,098
Financing Receivable, Troubled Debt Restructuring, Postmodification	$ 18,212	$ 1,106
Commercial And Industrial [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts \| contract	1	2
Financing Receivable, Troubled Debt Restructuring, Premodification	$ 14,148	$ 268
Financing Receivable, Troubled Debt Restructuring, Postmodification	$ 14,148	$ 268
Commercial Real Estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts \| contract	5	1
Financing Receivable, Troubled Debt Restructuring, Premodification	$ 3,964	$ 604
Financing Receivable, Troubled Debt Restructuring, Postmodification	$ 3,964	$ 604
Small Business [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts \| contract	1	1
Financing Receivable, Troubled Debt Restructuring, Premodification	$ 100	$ 49
Financing Receivable, Troubled Debt Restructuring, Postmodification	$ 100	$ 25
Residential Real Estate [Member]
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Modifications, Number of Contracts \| contract		1
Financing Receivable, Troubled Debt Restructuring, Premodification		$ 177
Financing Receivable, Troubled Debt Restructuring, Postmodification		$ 209

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.

No definition available.

+ Details

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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

- Details

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