Derivatives and Hedging Activities (Derivative Financial Instruments included in OCI and Current Earnings) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax	$ (763)	$ 2,329	$ (795)	$ 5,785
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	(1,191)	(2,509)	(2,558)	(5,179)
Derivatives designated as hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, before Tax	(1,191)	(2,509)	(2,558)	(5,179)
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Other income	(30)	79	68	223
Location, Statement of Income, Balance [Axis]: us-gaap:NoninterestIncomeOtherOperatingIncome | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Other income	29	16	61	52
Location, Statement of Income, Balance [Axis]: us-gaap:OtherNoninterestExpense | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Other income	(19)	(29)	(41)	(46)
Location, Statement of Income, Balance [Axis]: indb:FeesAndCommissionMortgageBanking | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Mortgage banking income	(40)	92	48	217
Derivatives designated as hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax	$ (763)	$ 2,329	$ (795)	$ 5,785