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Profit Sharing Plan (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred Compensation Arrangements [Abstract]
Maximum percentage of compensation employee is allowed to contribute	15.00%mcy_MaximumPercentageOfCompensationEmployeeIsAllowedToContribute
Matching contributions	$ 8.0us-gaap_DeferredCompensationArrangementWithIndividualEmployerContribution	$ 8.1us-gaap_DeferredCompensationArrangementWithIndividualEmployerContribution	$ 7.2us-gaap_DeferredCompensationArrangementWithIndividualEmployerContribution
Deferred Compensation Arrangement with Individual, Cash Award Granted, Amount	$ 19.2mcy_IndividualEmployeesBonusExpenseCash	$ 0mcy_IndividualEmployeesBonusExpenseCash	$ 10.0mcy_IndividualEmployeesBonusExpenseCash

X

- Definition

Individual Employees, Bonus Expense, Cash

+ References

No definition available.

+ Details

Name:	mcy_IndividualEmployeesBonusExpenseCash
Namespace Prefix:	mcy_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Maximum percentage of compensation employee is allowed to contribute to the Plan.

+ References

No definition available.

+ Details

Name:	mcy_MaximumPercentageOfCompensationEmployeeIsAllowedToContribute
Namespace Prefix:	mcy_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_DeferredCompensationArrangementsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The amount of payment into the fund established for purposes of making future disbursements to the individual in accordance with the terms and understanding of the deferred compensation arrangement.

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualEmployerContribution
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration