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Commitments and contingencies Financial Instruments with Off-Balance Sheet Risk (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Commitments to Extend Credit [Member]    
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]    
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability $ 1,862,493us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommitmentsToExtendCreditMember		 $ 1,822,369us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability
/ us-gaap_FinancialInstrumentAxis
= us-gaap_CommitmentsToExtendCreditMember
Standby Letters of Credit [Member]    
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]    
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability 19,912us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability
/ us-gaap_FinancialInstrumentAxis
= us-gaap_StandbyLettersOfCreditMember		 18,516us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability
/ us-gaap_FinancialInstrumentAxis
= us-gaap_StandbyLettersOfCreditMember
Deferred standby letter of credit fees [Member]    
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]    
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability $ 119us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability
/ us-gaap_FinancialInstrumentAxis
= indb_DeferredstandbyletterofcreditfeesMember		 $ 105us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability
/ us-gaap_FinancialInstrumentAxis
= indb_DeferredstandbyletterofcreditfeesMember