Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Reconciliation of fair value of securities
Available for sale Securities, Amortized Cost	$ 311,756	$ 294,996
Available for sale Securities, Gross Unrealized Gains	16,730	16,916
Available for sale Securities, Unrealized Losses Other	(2,572)	(3,308)
Available for sale Securities, Other Than Temporary Impairment	(2,758)	(3,272)
Available for sale Securities, Fair Value, Total	323,156	305,332
Held to maturity Securities, Amortized Cost	186,842	204,956
Held to maturity Securities, Gross Unrealized Gains	8,612	7,207
Held to maturity Securities, Unrealized Losses Other		(669)
Held to maturity Securities, Other Than Temporary Impairment
Held to Maturity, Fair Value, Total	195,454	211,494
Amortized Cost	498,598	499,952
Gross Unrealized Gains	25,342	24,123
Unrealized Losses Other	(2,572)	(3,977)
Other Than Temporary Impairment	(2,758)	(3,272)
Fair Value	518,610	516,826
U. S. Government Agency Securities [Member]
Reconciliation of fair value of securities
Available for sale Securities, Amortized Cost	20,055
Available for sale Securities, Gross Unrealized Gains	852
Available for sale Securities, Unrealized Losses Other
Available for sale Securities, Other Than Temporary Impairment
Available for sale Securities, Fair Value, Total	20,907
U.S. Treasury Securities [Member]
Reconciliation of fair value of securities
Held to maturity Securities, Amortized Cost	1,013	1,014
Held to maturity Securities, Gross Unrealized Gains	130	103
Held to maturity Securities, Unrealized Losses Other
Held to maturity Securities, Other Than Temporary Impairment
Held to Maturity, Fair Value, Total	1,143	1,117
Agency Mortgage-Backed Securities [Member]
Reconciliation of fair value of securities
Available for sale Securities, Amortized Cost	196,930	222,349
Available for sale Securities, Gross Unrealized Gains	14,833	16,042
Available for sale Securities, Unrealized Losses Other	(18)
Available for sale Securities, Other Than Temporary Impairment
Available for sale Securities, Fair Value, Total	211,745	238,391
Held to maturity Securities, Amortized Cost	81,523	109,553
Held to maturity Securities, Gross Unrealized Gains	5,239	4,406
Held to maturity Securities, Unrealized Losses Other
Held to maturity Securities, Other Than Temporary Impairment
Held to Maturity, Fair Value, Total	86,762	113,959
Agency Collateralized Mortgage Obligations [Member]
Reconciliation of fair value of securities
Available for sale Securities, Amortized Cost	72,621	52,927
Available for sale Securities, Gross Unrealized Gains	826	874
Available for sale Securities, Unrealized Losses Other	(75)
Available for sale Securities, Other Than Temporary Impairment
Available for sale Securities, Fair Value, Total	73,372	53,801
Held to maturity Securities, Amortized Cost	91,845	77,804
Held to maturity Securities, Gross Unrealized Gains	2,924	2,494
Held to maturity Securities, Unrealized Losses Other
Held to maturity Securities, Other Than Temporary Impairment
Held to Maturity, Fair Value, Total	94,769	80,298
State, County, and Municipal Securities [Member]
Reconciliation of fair value of securities
Held to maturity Securities, Amortized Cost	915	3,576
Held to maturity Securities, Gross Unrealized Gains	14	34
Held to maturity Securities, Unrealized Losses Other
Held to maturity Securities, Other Than Temporary Impairment
Held to Maturity, Fair Value, Total	929	3,610
Private Mortgage-Backed Securities [Member]
Reconciliation of fair value of securities
Available for sale Securities, Amortized Cost	3,935	6,215
Available for sale Securities, Gross Unrealized Gains
Available for sale Securities, Unrealized Losses Other
Available for sale Securities, Other Than Temporary Impairment	177	(105)
Available for sale Securities, Fair Value, Total	4,112	6,110
Single Issuer Trust Preferred Securities Issued by Banks and Insurers [Member]
Reconciliation of fair value of securities
Available for sale Securities, Amortized Cost		5,000
Available for sale Securities, Gross Unrealized Gains
Available for sale Securities, Unrealized Losses Other		(790)
Available for sale Securities, Other Than Temporary Impairment
Available for sale Securities, Fair Value, Total		4,210
Held to maturity Securities, Amortized Cost	6,538	8,000
Held to maturity Securities, Gross Unrealized Gains	63	15
Held to maturity Securities, Unrealized Losses Other		(669)
Held to maturity Securities, Other Than Temporary Impairment
Held to Maturity, Fair Value, Total	6,601	7,346
Pooled Trust Preferred Securities Issued by Banks and Insurers [Member]
Reconciliation of fair value of securities
Available for sale Securities, Amortized Cost	8,451	8,505
Available for sale Securities, Gross Unrealized Gains
Available for sale Securities, Unrealized Losses Other	(2,464)	(2,518)
Available for sale Securities, Other Than Temporary Impairment	(2,935)	(3,167)
Available for sale Securities, Fair Value, Total	3,052	2,820
Marketable Equity Securities [Member]
Reconciliation of fair value of securities
Available for sale Securities, Amortized Cost	9,764
Available for sale Securities, Gross Unrealized Gains	219
Available for sale Securities, Unrealized Losses Other	(15)
Available for sale Securities, Other Than Temporary Impairment
Available for sale Securities, Fair Value, Total	9,968
Corporate Debt Securities [Member]
Reconciliation of fair value of securities
Held to maturity Securities, Amortized Cost	5,008	5,009
Held to maturity Securities, Gross Unrealized Gains	242	155
Held to maturity Securities, Unrealized Losses Other
Held to maturity Securities, Other Than Temporary Impairment
Held to Maturity, Fair Value, Total	$ 5,250	$ 5,164

Available for sale securities and held to maturity securities amortized cost.

No definition available.

Name:	indb_AvailableForSaleSecuritiesAndHeldToMaturitySecuritiesAmortizedCost
Namespace Prefix:	indb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Available for sale securities and held to maturity securities gross unrealized gains.

+ References

No definition available.

+ Details

Name:	indb_AvailableForSaleSecuritiesAndHeldToMaturitySecuritiesGrossUnrealizedGains
Namespace Prefix:	indb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Available for sale securities and held to maturity securities gross unrealized losses.

+ References

No definition available.

+ Details

Name:	indb_AvailableForSaleSecuritiesAndHeldToMaturitySecuritiesGrossUnrealizedLosses
Namespace Prefix:	indb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This item represents the gross unrealized losses for securities, net of any other-than-temporary impairment losses at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

+ Details

Name:	indb_AvailableForSaleSecuritiesGrossUnrealizedLossesNetOfOtherThanTemporaryImpairmentLosses
Namespace Prefix:	indb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Available-for-sale securities, other-than-temporary impairment unrealized losses, portion recognized in other comprehensive income.

+ References

No definition available.

+ Details

Name:	indb_AvailableForSaleSecuritiesOtherThanTemporaryImpairmentUnrealizedLossesPortionRecognizedInOtherComprehensiveIncome
Namespace Prefix:	indb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Held-to-maturity securities, other-than-temporary impairment unrealized losses, portion recognized in other comprehensive income.

+ References

No definition available.

+ Details

Name:	indb_HeldToMaturitySecuritiesOtherThanTemporaryImpairmentUnrealizedLossesPortionRecognizedInOtherComprehensiveIncome
Namespace Prefix:	indb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Other than temporary impairment losses investments available for sale securities and held to maturity securities.

+ References

No definition available.

+ Details

Name:	indb_OtherThanTemporaryImpairmentLossesInvestmentsAvailableForSaleSecuritiesAndHeldToMaturitySecurities
Namespace Prefix:	indb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15E

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 7

-Footnote 2

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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

- Definition

Amount of debt and equity financial instruments classified as either held-to-maturity or available-for-sale.

+ References

No definition available.

+ Details

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

- Details

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

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27161-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13, 19

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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

- Definition

Amount of investments in debt securities categorized as held-to-maturity valued at amortized cost, excludes other than temporary impairment (OTTI).

+ References

No definition available.

+ Details

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

- Definition

This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 137

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27232-111563

+ Details

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

- Definition

As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 137

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27232-111563

+ Details

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

- Definition

As of the balance sheet date, the excess of carrying value (amortized cost) over fair value of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 19

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 137

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27232-111563

+ Details

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