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Fair Value Measurements and Disclosures - Valuation Techniques for Level 3 interest rate lock (Details) - Interest rate lock commitments - Level 3 $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2021 USD ($) | Sep. 30, 2020 USD ($) | Sep. 30, 2021 USD ($) | Sep. 30, 2020 USD ($) | Dec. 31, 2020 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |
Derivative asset | $ 1,712 |  | $ 1,712 |  | $ 6,932
Valuation technique extensible list | us-gaap:ValuationTechniqueConsensusPricingModelMember |  | us-gaap:ValuationTechniqueConsensusPricingModelMember |  | us-gaap:ValuationTechniqueConsensusPricingModelMember
Measurement input extensible list | mrbk:LoanOriginationSucessRateMember |  | mrbk:LoanOriginationSucessRateMember |  | mrbk:LoanOriginationSucessRateMember
Net realized gains (losses) | $ (1,100) | $ 3,200 | $ (5,500) | $ 7,200 |
Minimum |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |
Measurement input | 1 |  | 1 |  | 1
Maximum |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |
Measurement input | 99 |  | 99 |  | 99
Weighted Average |  |  |  |  |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |  |  |  |  |
Measurement input | 87.26 |  | 87.26 |  | 83.08

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- Definition Value of input used to measure derivative asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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- Definition Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313 Reference 2: 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=121572278&loc=d3e13433-108611 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 + Details
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