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Fair Value of Financial Instruments (Narrative) (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]    
Unsecured Debt $ 150,000us-gaap_UnsecuredDebt $ 150,000us-gaap_UnsecuredDebt
Level 2 [Member] | Secured Notes One [Member]    
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]    
Secured notes 120,000us-gaap_SecuredDebt
/ us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis
= mcy_SecuredNotesOneMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
 
Level 2 [Member] | Secured Notes Two [Member]    
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]    
Secured notes $ 20,000us-gaap_SecuredDebt
/ us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis
= mcy_SecuredNotesTwoMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member