SECURITIES (Reconciliation of fair value of Available for Sale securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale, Amortized Cost	$ 1,566,779	$ 1,583,736
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	54	8,808
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(167,679)	(21,396)
Debt Securities, Available-for-Sale	1,399,154	1,571,148
Debt Securities, Available-for-Sale,	1,566,779	1,583,736
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale, Amortized Cost	230,936	217,393
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	990
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(28,636)	(2,901)
Debt Securities, Available-for-Sale	202,300	215,482
Debt Securities, Available-for-Sale,	230,936	217,393
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
US Treasury Securities [Member]
Debt Securities, Available-for-sale, Amortized Cost	874,035	873,467
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax		172
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(82,694)	(12,191)
Debt Securities, Available-for-Sale	791,341	861,448
Debt Securities, Available-for-Sale,	874,035	873,467
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale, Amortized Cost	359,068	364,955
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	54	4,512
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(45,434)	(5,534)
Debt Securities, Available-for-Sale	313,688	363,933
Debt Securities, Available-for-Sale,	359,068	364,955
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
Agency collateralized mortgage obligations [Member]
Debt Securities, Available-for-sale, Amortized Cost	41,874	78,966
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax		1,282
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(3,031)	(571)
Debt Securities, Available-for-Sale	38,843	79,677
Debt Securities, Available-for-Sale,	41,874	78,966
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale, Amortized Cost	193	192
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax		11
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(2)	0
Debt Securities, Available-for-Sale	191	203
Debt Securities, Available-for-Sale,	193	192
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
Single issuer trust preferred securities issued by banks [Member]
Debt Securities, Available-for-sale, Amortized Cost	0	489
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	2
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Debt Securities, Available-for-Sale		491
Debt Securities, Available-for-Sale,	0	489
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
Pooled Trust Preferred Securities Issued By Banks And Insurers [Member]
Debt Securities, Available-for-sale, Amortized Cost	1,203	1,199
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(169)	(199)
Debt Securities, Available-for-Sale	1,034	1,000
Debt Securities, Available-for-Sale,	1,203	1,199
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	0	0
Small Business Administration Pooled Securities [Member]
Debt Securities, Available-for-sale, Amortized Cost	59,470	47,075
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	1,839
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(7,713)	0
Debt Securities, Available-for-Sale	51,757	48,914
Debt Securities, Available-for-Sale,	59,470	47,075
Debt Securities, Available-for-Sale, Allowance for Credit Loss, Excluding Accrued Interest	$ 0	$ 0

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

+ Details

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

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

+ Details

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

- Definition

Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

+ Details

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

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

+ Details

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

- Definition

Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CollateralizedDebtObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_TrustPreferredSecuritiesSubjectToMandatoryRedemptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=indb_PooledTrustPreferredSecuritiesIssuedByBanksAndInsurersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=indb_SmallBusinessAdministrationPooledSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: