Credit Quality of Loans and Allowance for Loan Losses, Aggregate Allowance for Loan Losses and Related Party Lending (Details) (USD $)	3 Months Ended
Mar. 31, 2015 Segment	Dec. 31, 2014
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of industry segment concentration above threshold limit	1
Threshold percentage of loan portfolio (in hundredths)	10.00%us-gaap_ConcentrationRiskPercentage1
Loans exposure in oil and gas industry	$ 287,600,000msl_LoansExposureInOilAndGasIndustry
Exposure in oil and gas industry specified as percentage of total loans (in hundredths)	21.90%
Loans with exposure in commercial real estate	521,900,000
Loans on nonaccrual status	12,894,000	10,701,000
Commercial, Financial and Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans on nonaccrual status	2,413,000	2,642,000
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans with exposure in commercial real estate	471,700,000
Percentage of CRE loans secured by owner-occupied commercial properties (in hundredths)	55.00%
Loans on nonaccrual status	8,100,000
Nonaccrual status of loans specified as percentage of total CRE loans (in hundredths)	1.60%
Finance Leases Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans on nonaccrual status	0	0
Other [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans on nonaccrual status	$ 0	$ 0

This line item represents the exposure in the oil and gas industry specified as a percentage of total loans.

No definition available.

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

- 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

Name:	msl_LoansWithExposureInCommercialRealEstate
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_NonaccrualStatusOfLoansSpecifiedAsPercentageOfTotalCreLoans
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

This line item represents the percentage of CRE loans secured by owner occupied commercial properties.

+ References

No definition available.

+ Details

Name:	msl_PercentageOfCRELoansSecuredByOwnerOccupiedCommercialProperties
Namespace Prefix:	msl_
Data Type:	num:percentItemType
Balance Type:	na
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://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems
Namespace Prefix:	us-gaap_
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://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5111-111524

+ Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=msl_OtherLoanReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_FinanceLeasesFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: