Fair Value Measurements and Disclosure - Valuation Techniques (Details) - Level 3 - Interest rate lock commitments	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset	$ 310,000
Derivative Asset, Valuation Technique [Extensible List]	us-gaap:ValuationTechniqueConsensusPricingModelMember
Derivative Asset, Measurement Input [Extensible List]	mrbk:LoanOriginationSucessRateMember
Gain in fair value of derivative asset	$ 40,000	$ 367,000
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