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Fair Value Measurement (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value Measurement [Line Items]
Percentage of portfolio of unadjusted fair values obtained	99.70%mcy_PercentageOfUnadjustedFairValueObtained
Percentage of portfolio of specific unadjusted broker quotes obtained	0.30%mcy_PercentageOfSpecificUnadjustedBrokerQuotesObtained
Minimum [Member]
Fair Value Measurement [Line Items]
Number of knowledgeable outside security brokers consulted to determine fair value	1mcy_NumberOfKnowledgeableOutsideSecurityBrokersConsultedToDetermineFairValue / us-gaap_RangeAxis = us-gaap_MinimumMember
Commercial Mortgage Backed Securities [Member] | Level 2 [Member]
Fair Value Measurement [Line Items]
Trading securities, fair value disclosure	32.5us-gaap_TradingSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialMortgageBackedSecuritiesMember	$ 21.9us-gaap_TradingSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialMortgageBackedSecuritiesMember

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.4)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789

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