Financial Instruments with Off Balance Sheet Risk, Commitments and Contingencies (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional Amount	$ 139,614,000	$ 66,566,000
Indemnification or Repurchase of loan	0
Provision for loan losses	71,000	68,000
Loan receivables repurchased	$ 0
Minimum
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Repurchase or Indemnification Term of Loan	2 months
Delinquency period of loan	6 months
Maximum
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Repurchase or Indemnification Term of Loan	3 months
Commitments to extend credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet financial instruments	$ 327,788,000	290,614,000
Mortgage Loans Commitments
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet financial instruments	$ 72,900,000	33,400,000
Mortgage Loans Commitments \| Minimum
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commitment term	30 days
Mortgage Loans Commitments \| Maximum
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commitment term	90 days
Letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Off-balance sheet financial instruments	$ 9,750,000	5,158,000
Commitment term	12 months
Forward Commitments
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Commitment term	90 days
Notional Amount	$ 62,750,000	26,500,000
Forward Sale Of Mortgage Backed Securities
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional Amount	62,800,000	26,500,000
Forward Best Effort Sale Commitment
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional Amount	$ 18,600,000	$ 9,300,000

Period of time between a commitment and the maturity of that commitment.

No definition available.

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Namespace Prefix:	mrbk_
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Balance Type:	na
Period Type:	duration

- Definition

The delinquency period of loan.

+ References

No definition available.

+ Details

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Namespace Prefix:	mrbk_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of indemnification or repurchase of loan.

+ References

No definition available.

+ Details

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

- Definition

The payment for loans receivable that were sold and then subsequently repurchased.

+ References

No definition available.

+ Details

Name:	mrbk_LoanReceivableSoldRepurchased
Namespace Prefix:	mrbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The term of repurchase or indemnification if the loan is delinquent during a set period.

+ References

No definition available.

+ Details

Name:	mrbk_RepurchaseOrIndemnificationTermOfLoan
Namespace Prefix:	mrbk_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The fair value of financial liabilities, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13433-108611

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

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

- Definition

Amount of credit loss expense (reversal of expense) for financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-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 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(11))
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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- Details

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- Details

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Namespace Prefix:
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- Details

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- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
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- Details

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