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Income Taxes (Details) (USD $)
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Income Tax Disclosure [Abstract]      
Income tax provision $ 20,225,000us-gaap_IncomeTaxExpenseBenefit $ 26,227,000us-gaap_IncomeTaxExpenseBenefit  
Effective income tax rates 37.80%eme_EffectiveIncomeTaxRateBeforeDiscreteItems 37.60%eme_EffectiveIncomeTaxRateBeforeDiscreteItems  
Actual income tax rates 37.90%us-gaap_EffectiveIncomeTaxRateContinuingOperations 37.70%us-gaap_EffectiveIncomeTaxRateContinuingOperations  
Unrecognized income tax benefits 5,200,000us-gaap_UnrecognizedTaxBenefits   5,200,000us-gaap_UnrecognizedTaxBenefits
Unrecognized income tax benefits, if recognized, that would favorably affect the effective income tax rate 3,000,000us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate   3,000,000us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate
Accrued interest expense related to unrecognized income tax benefits 400,000us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued   300,000us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued
Interest expense related to unrecognized income tax benefits 100,000us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense    
Interest income related to unrecognized income tax benefits   100,000eme_UnrecognizedTaxBenefitsInterestincomeOnIncomeTaxes  
Unrecognized income tax benefits to be recognized in the next twelve months $ 3,300,000us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleAmountOfUnrecordedBenefit