This line item represents the interest received on nonaccrual loans.

No definition available.

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Namespace Prefix:	msl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This line item represents the loans exposure in the oil and gas industry.

+ References

No definition available.

+ Details

Name:	msl_LoansExposureInOilAndGasIndustry
Namespace Prefix:	msl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This line item represents the loans with exposure in the commercial real estate section.

+ References

No definition available.

+ Details

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Namespace Prefix:	msl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This line item represents the percentage of nonaccrual status of loans specified as percentage of total CRE loans.

+ References

No definition available.

+ Details

Name:	msl_NonaccrualStatusofLoansSpecifiedasaPercentageofTotalCRELoans
Namespace Prefix:	msl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This line item represents the number of industry segment concentration above threshold limit of the loan portfolio.

+ References

No definition available.

+ Details

Name:	msl_NumberOfIndustrySegmentConcentrationAboveThresholdLimit
Namespace Prefix:	msl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Total CRE loans on non-accrual

+ References

No definition available.

+ Details

Name:	msl_TotalCREloansonnonaccrual
Namespace Prefix:	msl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Recorded investment in financing receivables that are on nonaccrual status 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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-SubTopic 10
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Reflects the unfunded portion of contractual agreements to lend funds to borrowers for loans whose terms have been modified by troubled debt restructuring.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
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Name:	us-gaap_LoansAndLeasesReceivableImpairedCommitmentToLend
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

+ References

+ Details

Name:	us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Balance Type:
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Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
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Name:	us-gaap_ClassOfFinancingReceivableTypeOfBorrowerAxis=msl_OwnerOccupiedCommercialPropertyMember
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Credit Quality of Loans and Allowance for Loan Losses - Narrative (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) contract	Jun. 30, 2017 contract	Jun. 30, 2018 USD ($) industry_concentration contract	Jun. 30, 2017 USD ($) contract	Dec. 31, 2017 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Number of industry segment concentration above threshold limit \| industry_concentration			1
Concentration risk (as a percent)			10.00%
Loans exposure in oil and gas industry	$ 153,600,000		$ 153,600,000
Loans with exposure in commercial real estate	481,000,000		481,000,000
Loans on nonaccrual status	$ 73,538,000		$ 73,538,000		$ 49,278,000
Nonaccrual status of loans specified as percentage of total CRE loans	6.50%		6.50%
Interest lost on nonaccrual loans			$ 3,400,000	$ 1,700,000
Interest received on nonaccrual loans			176,000	$ 195,000
Commitments to lend	$ 0		$ 0
Defaults on loans \| contract	0	0	0	1
Pre-modification balance				$ 2,000,000
Real estate – commercial
Financing Receivable, Recorded Investment [Line Items]
Total CRE loans on non-accrual	$ 31,400,000		$ 31,400,000
Loans on nonaccrual status	$ 29,916,000		$ 29,916,000		$ 11,128,000
Loans and Finance Receivables \| Customer Concentration Risk \| Manufacturing Industry
Financing Receivable, Recorded Investment [Line Items]
Concentration risk (as a percent)			14.50%
Loans and Finance Receivables \| Customer Concentration Risk \| Real estate – commercial
Financing Receivable, Recorded Investment [Line Items]
Concentration risk (as a percent)			45.50%
Loans and Finance Receivables \| Customer Concentration Risk \| Real estate – commercial \| Owner Occupied Commercial Property
Financing Receivable, Recorded Investment [Line Items]
Concentration risk (as a percent)			52.00%