Allowance for Loan Losses (the Allowance) - Allowance allocated by portfolio segment (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Impaired Loans
Allowance on loans and leases individually evaluated for impairment	$ 57	$ 136
Allowance on loans and leases collectively evaluated for impairment	11,041	9,377
Total	11,098	9,513	$ 8,376	$ 8,053
Carrying value of loans and leases individually evaluated for impairment	9,156	7,307
Carrying value of loans and leases collectively evaluated for impairment	1,003,726	948,646
Total	1,012,882	955,953
Commercial mortgage
Impaired Loans
Allowance on loans and leases collectively evaluated for impairment	4,112	3,426
Total	4,112	3,426	3,163	3,209
Carrying value of loans and leases individually evaluated for impairment	2,117	2,138
Carrying value of loans and leases collectively evaluated for impairment	389,211	360,452
Total	391,328	362,590
Home equity lines and loans
Impaired Loans
Allowance on loans and leases individually evaluated for impairment	36	46
Allowance on loans and leases collectively evaluated for impairment	448	296
Total	484	342	341	323
Carrying value of loans and leases individually evaluated for impairment	761	536
Carrying value of loans and leases collectively evaluated for impairment	78,003	81,047
Total	78,764	81,583
Residential mortgage
Impaired Loans
Allowance on loans and leases collectively evaluated for impairment	219	179
Total	219	179	212	191
Carrying value of loans and leases individually evaluated for impairment	3,804	854
Carrying value of loans and leases collectively evaluated for impairment	38,297	42,265
Total	42,101	43,119
Construction
Impaired Loans
Allowance on loans and leases collectively evaluated for impairment	2,381	2,362
Total	2,381	2,362	1,802	1,627
Carrying value of loans and leases individually evaluated for impairment	1,231	1,247
Carrying value of loans and leases collectively evaluated for impairment	174,133	170,797
Total	175,364	172,044
Commercial and industrial
Impaired Loans
Allowance on loans and leases individually evaluated for impairment	21	27
Allowance on loans and leases collectively evaluated for impairment	3,148	2,657
Total	3,169	2,684	2,760	2,612
Carrying value of loans and leases individually evaluated for impairment	1,015	1,288
Carrying value of loans and leases collectively evaluated for impairment	291,408	272,013
Total	292,423	273,301
Small Business Loans
Impaired Loans
Allowance on loans and leases individually evaluated for impairment		63
Allowance on loans and leases collectively evaluated for impairment	725	446
Total	725	509	86	78
Carrying value of loans and leases individually evaluated for impairment	228	1,244
Carrying value of loans and leases collectively evaluated for impairment	31,545	20,372
Total	31,773	21,616
Consumer
Impaired Loans
Allowance on loans and leases collectively evaluated for impairment	4	6
Total	4	6	4	3
Carrying value of loans and leases collectively evaluated for impairment	570	1,003
Total	570	1,003
Leases
Impaired Loans
Allowance on loans and leases collectively evaluated for impairment	4	5
Total	4	5	$ 8	$ 10
Carrying value of loans and leases collectively evaluated for impairment	559	697
Total	$ 559	$ 697

The balance of financing receivables excluding loans and leases carried at fair value.

No definition available.

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

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

+ Details

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

+ Details

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

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
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://fasb.org/us-gaap/role/ref/legacyRef
-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 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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=118939070&loc=d3e15032-111544

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-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

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=mrbk_CommercialMortgageMember
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=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: