Derivative Financial Instruments (Q3) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative financial instrument according to type of hedge[ Abstract]
Expected unrealized loss on cash flow hedges to be reclassified in the next twelve months	$ (30)
The maximum term of cash flow hedge	3 years 10 months 24 days
Fair value of derivative instruments, balance sheet location [Abstract]
Asset Derivatives	$ 1,973	$ 2,251	$ 1,238
Liability Derivatives	1,073	975	619
Cash Flow Hedge [Member] \| Pay-fixed Interest Rate Swap [Member]
Derivative financial instrument according to type of hedge[ Abstract]
Notional Amount	$ 15,000
Average Maturity	3 years 10 months 24 days
Fair Value	$ 105
No Hedge Designation [Member]
Derivative financial instrument according to type of hedge[ Abstract]
Notional Amount	$ 222,740	$ 187,092	$ 126,271
Average Maturity	3 years 6 months	4 years 4 months 24 days	3 years 8 months 12 days
Fair Value	$ 795	$ 1,276	$ 619
Fair value of derivative instruments, balance sheet location [Abstract]
Asset Derivatives	1,868	2,251
Liability Derivatives	1,073	975
No Hedge Designation [Member] \| Rate-Lock Mortgage Loan Commitments [Member]
Derivative financial instrument according to type of hedge[ Abstract]
Notional Amount	$ 36,580	$ 26,658	$ 20,581
Average Maturity	1 month 6 days	1 month 6 days	1 month 6 days
Fair Value	$ 769	$ 646	$ 550
No Hedge Designation [Member] \| Mandatory Commitments to Sell Mortgage Loans [Member]
Derivative financial instrument according to type of hedge[ Abstract]
Notional Amount	$ 74,750	$ 61,954	$ 46,320
Average Maturity	1 month 6 days	1 month 6 days	1 month 6 days
Fair Value	$ 26	$ 630	$ 69
No Hedge Designation [Member] \| Pay-fixed Interest Rate Swap [Member]
Derivative financial instrument according to type of hedge[ Abstract]
Notional Amount	$ 52,586	$ 46,121
Average Maturity	7 years 1 month 6 days	8 years 7 months 6 days
Fair Value	$ 52	$ 249
No Hedge Designation [Member] \| Pay-variable Interest Rate Swap [Member]
Derivative financial instrument according to type of hedge[ Abstract]
Notional Amount	$ 52,586	$ 46,121
Average Maturity	7 years 1 month 6 days	8 years 7 months 6 days
Fair Value	$ (52)	$ (249)
No Hedge Designation [Member] \| Purchased Options [Member]
Derivative financial instrument according to type of hedge[ Abstract]
Notional Amount	$ 3,119	$ 3,119	$ 2,098
Average Maturity	3 years 9 months 18 days	4 years 6 months	5 years 8 months 12 days
Fair Value	$ 277	$ 238	$ 122
No Hedge Designation [Member] \| Written Options [Member]
Derivative financial instrument according to type of hedge[ Abstract]
Notional Amount	$ 3,119	$ 3,119	$ 2,098
Average Maturity	3 years 9 months 18 days	4 years 6 months	5 years 8 months 12 days
Fair Value	$ (277)	$ (238)	$ (122)
Other Assets [Member] \| Designated as Hedging Instrument [Member] \| Pay-fixed Interest Rate Swap [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Asset Derivatives	105	0
Other Assets [Member] \| No Hedge Designation [Member] \| Rate-Lock Mortgage Loan Commitments [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Asset Derivatives	769	646	550
Other Assets [Member] \| No Hedge Designation [Member] \| Mandatory Commitments to Sell Mortgage Loans [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Asset Derivatives	26	630	69
Other Assets [Member] \| No Hedge Designation [Member] \| Pay-fixed Interest Rate Swap [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Asset Derivatives	424	493
Other Assets [Member] \| No Hedge Designation [Member] \| Pay-variable Interest Rate Swap [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Asset Derivatives	372	244
Other Assets [Member] \| No Hedge Designation [Member] \| Purchased Options [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Asset Derivatives	277	238	122
Other Assets [Member] \| No Hedge Designation [Member] \| Written Options [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Asset Derivatives	0	0	0
Other Liabilities [Member] \| Designated as Hedging Instrument [Member] \| Pay-fixed Interest Rate Swap [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Liability Derivatives	0	0
Other Liabilities [Member] \| No Hedge Designation [Member] \| Rate-Lock Mortgage Loan Commitments [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Liability Derivatives	0	0	0
Other Liabilities [Member] \| No Hedge Designation [Member] \| Mandatory Commitments to Sell Mortgage Loans [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Liability Derivatives	0	0	0
Other Liabilities [Member] \| No Hedge Designation [Member] \| Pay-fixed Interest Rate Swap [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Liability Derivatives	372	244
Other Liabilities [Member] \| No Hedge Designation [Member] \| Pay-variable Interest Rate Swap [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Liability Derivatives	424	493
Other Liabilities [Member] \| No Hedge Designation [Member] \| Purchased Options [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Liability Derivatives	0	0	0
Other Liabilities [Member] \| No Hedge Designation [Member] \| Written Options [Member]
Fair value of derivative instruments, balance sheet location [Abstract]
Liability Derivatives	$ 277	$ 238	$ 122

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

+ Details

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

- Definition

Nominal or face amount used to calculate payments on the derivative asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

+ Details

Name:	us-gaap_DerivativeAssetNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeAverageRemainingMaturity1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226000-175313

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=SL51823488-111719

+ Details

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

- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=SL51823488-111719

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226000-175313

+ Details

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

- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13495-108611

+ Details

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

- References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Maximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

+ Details

Name:	us-gaap_MaximumLengthOfTimeHedgedInCashFlowHedge1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ibcp_InterestRateSwapPayFixedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateLockCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ibcp_MandatoryCommitmentsToSellMortgageLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ibcp_InterestRateSwapPayVariableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ibcp_PurchasedOptionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ibcp_WrittenOptionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: