COMMITMENTS, CONTINGENCIES AND CREDIT RISK - Maturities (Details) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2020	Dec. 31, 2019	Jan. 01, 2020
Anticipated material loss	$ 0
ACL for off-balance sheet credit exposures	2,400,000		$ 1,507,000
Losses as a result of make whole requests and loan repurchases	0	$ 0
Liability for unresolved repurchase demands	289,000	289,000
Commitments to extend credit
Loan commitments	728,472,000	725,506,000
Financial guarantees - standby letters of credit
Loan commitments	$ 55,676,000	$ 106,678,000

Represents the liability for unresolved repurchase demands.

No definition available.

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Namespace Prefix:	msbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The minimum amount the entity agreed to spend under the loan commitment.

+ References

No definition available.

+ Details

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Namespace Prefix:	msbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Balance Type:	debit
Period Type:	instant

- Definition

The amount of loss pertaining to the specified contingency that was charged against earnings in the period, including the effects of revisions in previously reported estimates.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of expected credit loss for credit exposure on off-balance-sheet commitment, including but not limited to, loan commitment, standby letter of credit, financial guarantee not accounted for as insurance. Excludes off-balance sheet credit exposure accounted for as insurance and instrument accounted for under derivatives and hedging.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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+ Details

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

- Details

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Period Type:

- Details

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