Loans Receivable - Age analysis of past due loans and leases (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Age Analysis of Past Due Loans and Leases
Total past due	$ 3,704	$ 5,043
Current	1,278,122	958,221
Total Accruing Loans and leases	1,281,826	963,264
Nonaccrual loans and leases	7,930	3,235
Loans and Leases Receivable, Gross, Total	$ 1,289,756	$ 966,499
Delinquency percentage	0.90%	0.86%
Loans at fair value	$ 12,182	$ 10,546
Commercial mortgage
Age Analysis of Past Due Loans and Leases
Current	482,042	361,857
Total Accruing Loans and leases	482,042	361,857
Nonaccrual loans and leases	3,061	733
Loans and Leases Receivable, Gross, Total	$ 485,103	$ 362,590
Delinquency percentage	0.63%	0.20%
Home equity lines and loans
Age Analysis of Past Due Loans and Leases
Current	$ 64,128	$ 81,046
Total Accruing Loans and leases	64,128	81,046
Nonaccrual loans and leases	859	537
Loans and Leases Receivable, Gross, Total	$ 64,987	$ 81,583
Delinquency percentage	1.32%	0.66%
Residential mortgage
Age Analysis of Past Due Loans and Leases
Total past due	$ 3,595	$ 4,675
Current	46,134	47,446
Total Accruing Loans and leases	49,729	52,121
Nonaccrual loans and leases	2,725	1,544
Loans and Leases Receivable, Gross, Total	$ 52,454	$ 53,665
Delinquency percentage	12.05%	11.59%
Loans at fair value	$ 12,182	$ 10,546
Construction
Age Analysis of Past Due Loans and Leases
Current	140,246	172,044
Total Accruing Loans and leases	140,246	172,044
Loans and Leases Receivable, Gross, Total	140,246	172,044
Commercial and industrial, including leases
Age Analysis of Past Due Loans and Leases
Total past due		206
Current	260,465	272,674
Total Accruing Loans and leases	260,465	272,880
Nonaccrual loans and leases	1,285	421
Loans and Leases Receivable, Gross, Total	$ 261,750	$ 273,301
Delinquency percentage	0.49%	0.23%
Small business loans
Age Analysis of Past Due Loans and Leases
Current	$ 49,542	$ 21,616
Total Accruing Loans and leases	49,542	21,616
Loans and Leases Receivable, Gross, Total	49,542	21,616
MainStreet Lending Program Loans
Age Analysis of Past Due Loans and Leases
Current	580
Total Accruing Loans and leases	580
Loans and Leases Receivable, Gross, Total	580
Paycheck Protection Program loans
Age Analysis of Past Due Loans and Leases
Current	203,543
Total Accruing Loans and leases	203,543
Loans and Leases Receivable, Gross, Total	203,543
Consumer
Age Analysis of Past Due Loans and Leases
Current	511	1,003
Total Accruing Loans and leases	511	1,003
Loans and Leases Receivable, Gross, Total	511	1,003
Leases
Age Analysis of Past Due Loans and Leases
Total past due	109	162
Current	30,931	535
Total Accruing Loans and leases	31,040	697
Loans and Leases Receivable, Gross, Total	$ 31,040	$ 697
Delinquency percentage	0.35%	23.24%
Current \| Residential mortgage
Age Analysis of Past Due Loans and Leases
Loans at fair value	$ 10,314	$ 9,056
30-89 days past due
Age Analysis of Past Due Loans and Leases
Total past due	3,704	5,043
30-89 days past due \| Residential mortgage
Age Analysis of Past Due Loans and Leases
Total past due	3,595	4,675
Loans at fair value	958	786
30-89 days past due \| Commercial and industrial, including leases
Age Analysis of Past Due Loans and Leases
Total past due		206
30-89 days past due \| Leases
Age Analysis of Past Due Loans and Leases
Total past due	109	162
Nonaccrual \| Residential mortgage
Age Analysis of Past Due Loans and Leases
Loans at fair value	$ 910	$ 704

Recorded investment in financing receivables that are on accrual status as of the balance sheet date.

No definition available.

Name:	mrbk_FinancingReceivableRecordedInvestmentAccrualStatus
Namespace Prefix:	mrbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of mortgage loans held-for-investment.

+ References

No definition available.

+ Details

Name:	mrbk_MortgagesHeldForInvestmentFairValueDisclosure
Namespace Prefix:	mrbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of financing receivable balance that is past due.

+ References

No definition available.

+ Details

Name:	us-gaap_FinancingReceivablePercentPastDue1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of financing receivable not past due.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953401-111524

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 80
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922355-210448

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919253-210447

+ Details

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

- Definition

Amount of financing receivable on nonaccrual status.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5111-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919258-210447

+ Details

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

- Definition

Amount of financing receivable past due.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 80
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922355-210448

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919253-210447

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953401-111524

+ Details

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

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

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522

+ Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_HomeEquityLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialAndIndustrialSectorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=mrbk_SmallBusinessLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=mrbk_MainstreetLendingProgramLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=mrbk_SmallBusinessLoansPaycheckProtectionProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=mrbk_LeasesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivables1To29DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=mrbk_FinancingReceivables30To89DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=mrbk_FinancingReceivablesNonaccrualMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: