Credit Quality of Loans and Allowance for Loan Losses - Loan Portfolio and Concentrations (Details) $ in Thousands	6 Months Ended
Jun. 30, 2016 USD ($) industry_concentration	Dec. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)
Loan portfolio [Abstract]
Loans	$ 1,262,389	$ 1,263,645	$ 1,294,392
Less allowance for loan losses	(21,378)	(19,011)
Loans, net	$ 1,241,011	1,244,634
Number of industry segment concentration above threshold limit \| industry_concentration	1
Concentration risk, percentage	10.00%
Loans exposure in oil and gas industry	$ 249,800
Exposure in the oil and gas industry specified as percentage of total loans	19.80%
Loans with exposure in commercial real estate	$ 540,000
Loans on nonaccrual status	59,865	50,051
Commercial, financial and agricultural
Loan portfolio [Abstract]
Loans	456,264	454,028	471,397
Loans on nonaccrual status	29,676	27,705
Real estate - construction
Loan portfolio [Abstract]
Loans	96,331	74,952	79,176
Loans on nonaccrual status	34	37
Real estate – commercial
Loan portfolio [Abstract]
Loans	$ 463,142	471,141	469,022
Percentage of CRE loans secured by owner-occupied commercial properties	55.00%
Loans on nonaccrual status	$ 27,300	19,907
Nonaccrual status of loans specified as percentage of total CRE loans	5.10%
Real estate – residential
Loan portfolio [Abstract]
Loans	$ 148,379	149,064	153,820
Loans on nonaccrual status	2,384	1,998
Installment loans to individuals
Loan portfolio [Abstract]
Loans	94,522	111,009	113,626
Loans on nonaccrual status	471	404
Lease financing receivable
Loan portfolio [Abstract]
Loans	1,641	1,968	5,561
Loans on nonaccrual status	0	0
Other
Loan portfolio [Abstract]
Loans	2,110	1,483	$ 1,790
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_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

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 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6351-108592

Reference 2: 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=73719730&loc=d3e13531-108611

Reference 3: 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=64851502&loc=d3e6404-108592

Reference 4: 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=73719730&loc=d3e13537-108611

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

Reference 2: 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=66008989&loc=d3e5111-111524

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

+ Details

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

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5074-111524

+ Details

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

- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- References

No definition available.

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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