The amount of acquisition cost of a business combination allocated to deposits.

No definition available.

Name:	msfg_BusinessAcquisitionPurchasePriceAllocationDeposits
Namespace Prefix:	msfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of acquisition cost of a business combination allocated to loans receivable.

+ References

No definition available.

+ Details

Name:	msfg_BusinessAcquisitionPurchasePriceAllocationLoansReceivable
Namespace Prefix:	msfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the amount of acquisition cost of a business combination allocated to property.

+ References

No definition available.

+ Details

Name:	msfg_BusinessAcquisitionPurchasePriceAllocationProperty1
Namespace Prefix:	msfg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the term over which goodwill and intangible asset arising from a business combination will be deducted for tax purpose.

+ References

No definition available.

+ Details

Name:	msfg_BusinessAcquisitionTermOverWhichGoodwillAndIntangibleAssetWillBeDeductedForTaxPurpose
Namespace Prefix:	msfg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of branches acquired by the entity during the period.

+ References

No definition available.

+ Details

Name:	msfg_NumberOfBranchesAcquired
Namespace Prefix:	msfg_
Data Type:	xbrli:positiveIntegerItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, 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 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=73531572&loc=d3e1043-128460

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of identifiable intangible assets recognized as of the acquisition date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 55
-Paragraph 37
-URI http://asc.fasb.org/extlink&oid=73531372&loc=d3e2207-128464

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-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=73530397&loc=d3e4845-128472

+ Details

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

- Definition

The cash inflow associated with the acquisition of business during the period (for example, cash that was held by the acquired business).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3179-108585

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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-Publisher FASB
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=64834752&loc=SL49117168-202975

+ Details

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

- Details

Name:	us-gaap_BusinessAcquisitionAxis=msfg_OldNationalBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CoreDepositsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

ACQUISITIONS - Acquisition of Old National Bank Branches (Details) $ in Thousands		12 Months Ended
	Aug. 14, 2015 USD ($)	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
ACQUISITIONS
Goodwill		$ 101,315	$ 75,953	$ 73,450
Acquisition-related costs		$ 7,130	$ 731	$ 3,119
Old National Bank
ACQUISITIONS
Number of branches acquired \| item		5
Loans	$ 37,000
Deposits	99,000
Property	1,000
Goodwill	2,500
Cash received at purchase	57,000
Acquisition-related costs	$ 731
Intangible asset amortization period	10 years
Term over which goodwill and intangible asset will be deducted for tax purpose	15 years
Old National Bank \| Core deposit intangibles
ACQUISITIONS
Intangible asset	$ 1,200