Loans, Allowance for Loan Losses and Credit Quality (Int Inc. Recognized on Impaired Loans by Portfolio) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Interest income recognized on impaired loans
Average Recorded Investment	$ 60,280	$ 72,017
Interest Income Recognized	357	413
WITH NO RELATED ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	49,131	58,970
Interest Income Recognized	251	300
WITH AN ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	11,149	13,047
Interest Income Recognized	106	113
Commercial and Industrial [Member] \| WITH NO RELATED ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	30,198	33,784
Interest Income Recognized	35	31
Commercial and Industrial [Member] \| WITH AN ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	498	227
Interest Income Recognized	3	2
Commercial Real Estate [Member] \| WITH NO RELATED ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	8,873	14,855
Interest Income Recognized	104	157
Commercial Real Estate [Member] \| WITH AN ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	1,682	1,730
Interest Income Recognized	24	24
Construction Loans [Member] \| WITH NO RELATED ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	311
Interest Income Recognized	0
Small Business [Member] \| WITH NO RELATED ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	323	710
Interest Income Recognized	2	5
Small Business [Member] \| WITH AN ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	181	131
Interest Income Recognized	2	2
Residential Real Estate [Member] \| WITH NO RELATED ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	4,421	4,254
Interest Income Recognized	54	53
Residential Real Estate [Member] \| WITH AN ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	7,665	9,060
Interest Income Recognized	64	71
Consumer Home Equity [Member] \| WITH NO RELATED ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	4,952	5,280
Interest Income Recognized	55	53
Consumer Home Equity [Member] \| WITH AN ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	985	1,688
Interest Income Recognized	12	12
Consumer - Other [Member] \| WITH NO RELATED ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	53	87
Interest Income Recognized	1	1
Consumer - Other [Member] \| WITH AN ALLOWANCE RECORDED: [Member]
Interest income recognized on impaired loans
Average Recorded Investment	138	211
Interest Income Recognized	$ 1	$ 2

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 http://asc.fasb.org/extlink&oid=84173941&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 http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

Reference 2: 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 http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

+ Details

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

- Definition

Amount of interest income, recognized on cash basis, on financing receivables, for which there is no related allowance for credit losses and are recognized as impaired.

+ References

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of interest income on financing receivables, for which there is a related allowance for credit losses, recognized on a cash-basis method of accounting that the financing receivables were impaired.

+ References

+ Details

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

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=indb_WithNoRelatedAllowanceRecordedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=indb_WithAllowanceRecordedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- 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=us-gaap_ConstructionLoansMember
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:

- Details

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

- Details

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