Fair Value Measurements and Disclosures - Valuation Techniques for Level 3 interest rate lock (Details) - Interest rate lock commitments $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	$ 329
Valuation technique extensible list	us-gaap:ValuationTechniqueConsensusPricingModelMember
Measurement input extensible list	mrbk:LoanOriginationSucessRateMember
Loss in fair value of derivative assets	$ (19)	$ (242)
Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	1
Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	99
Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	89.27