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Debt - Narrative (Details) (USD $)
12 Months Ended 3 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2014
Nov. 24, 2013
Line of Credit Facility [Line Items]        
Interest rate description Borrowings under the 2013 Credit Agreement bear interest at (1) a rate which is the prime commercial lending rate announced by Bank of Montreal from time to time (3.25% at December 31, 2014) plus 0.25% to 0.75%, based on certain financial tests or (2) United States dollar LIBOR (0.17% at December 31, 2014) plus 1.25% to 1.75%, based on certain financial tests. The interest rate in effect at December 31, 2014 was 1.42%. Fees for letters of credit issued under the 2013 Revolving Credit Facility range from 1.25% to 1.75% of the respective face amounts of outstanding letters of credit and are computed based on certain financial tests.      
Letters of credit outstanding (in US dollars) $ 95,500,000us-gaap_LettersOfCreditOutstandingAmount $ 83,300,000us-gaap_LettersOfCreditOutstandingAmount $ 95,500,000us-gaap_LettersOfCreditOutstandingAmount  
2011 Credit Agreement        
Line of Credit Facility [Line Items]        
Line of credit facility maximum borrowing capacity (in US dollars)       750,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= eme_CreditAgreement2011Member
Write off of deferred debt issuance costs (in US dollars)   300,000us-gaap_WriteOffOfDeferredDebtIssuanceCost
/ us-gaap_DebtInstrumentAxis
= eme_CreditAgreement2011Member
   
2013 Credit Agreement        
Line of Credit Facility [Line Items]        
Expiration date of revolving credit facility Nov. 25, 2018      
Interest rate 1.42%us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
/ us-gaap_DebtInstrumentAxis
= eme_CreditAgreement2013MemberMember
  1.42%us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
/ us-gaap_DebtInstrumentAxis
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Debt issuance costs, capitalized (in US dollars)   3,000,000us-gaap_DeferredFinanceCostsGross
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2013 Revolving Credit Facility        
Line of Credit Facility [Line Items]        
Line of credit facility maximum borrowing capacity (in US dollars)   750,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= eme_RevolvingCreditFacility2013MemberMember
   
Increase in borrowing capacity (in US dollars) 1,050,000,000eme_IncreaseBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= eme_RevolvingCreditFacility2013MemberMember
  1,050,000,000eme_IncreaseBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
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Letters of credit maximum borrowing capacity (in US dollars) 250,000,000eme_LettersOfCreditMaximumBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= eme_RevolvingCreditFacility2013MemberMember
  250,000,000eme_LettersOfCreditMaximumBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= eme_RevolvingCreditFacility2013MemberMember
 
Commitment fee percentage of unused amount 0.20%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
/ us-gaap_DebtInstrumentAxis
= eme_RevolvingCreditFacility2013MemberMember
     
Borrowings under revolving credit facility (in US dollars) 0us-gaap_LongTermLineOfCredit
/ us-gaap_DebtInstrumentAxis
= eme_RevolvingCreditFacility2013MemberMember
0us-gaap_LongTermLineOfCredit
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0us-gaap_LongTermLineOfCredit
/ us-gaap_DebtInstrumentAxis
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2013 Term Loan        
Line of Credit Facility [Line Items]        
Term Loan (in US dollars) 332,500,000us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= eme_TermLoan2013Member
350,000,000us-gaap_LongTermDebt
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= eme_TermLoan2013Member
332,500,000us-gaap_LongTermDebt
/ us-gaap_DebtInstrumentAxis
= eme_TermLoan2013Member
 
Periodic principal payments on term loan (in US dollars)     $ 4,400,000us-gaap_DebtInstrumentPeriodicPaymentPrincipal
/ us-gaap_DebtInstrumentAxis
= eme_TermLoan2013Member
 
Minimum | 2013 Revolving Credit Facility        
Line of Credit Facility [Line Items]        
Commitment fee percentage of unused amount 0.20%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
/ us-gaap_DebtInstrumentAxis
= eme_RevolvingCreditFacility2013MemberMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
     
Letter of credit fees 1.25%eme_RangeOfLetterOfCreditFees
/ us-gaap_DebtInstrumentAxis
= eme_RevolvingCreditFacility2013MemberMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
  1.25%eme_RangeOfLetterOfCreditFees
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= eme_RevolvingCreditFacility2013MemberMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
 
Maximum | 2013 Revolving Credit Facility        
Line of Credit Facility [Line Items]        
Commitment fee percentage of unused amount 0.30%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
/ us-gaap_DebtInstrumentAxis
= eme_RevolvingCreditFacility2013MemberMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
     
Letter of credit fees 1.75%eme_RangeOfLetterOfCreditFees
/ us-gaap_DebtInstrumentAxis
= eme_RevolvingCreditFacility2013MemberMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
  1.75%eme_RangeOfLetterOfCreditFees
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/ us-gaap_RangeAxis
= us-gaap_MaximumMember
 
Prime Rate | 2013 Credit Agreement        
Line of Credit Facility [Line Items]        
Commercial lending rate 3.25%us-gaap_LongTermDebtPercentageBearingVariableInterestRate
/ us-gaap_DebtInstrumentAxis
= eme_CreditAgreement2013MemberMember
/ us-gaap_VariableRateAxis
= us-gaap_PrimeRateMember
  3.25%us-gaap_LongTermDebtPercentageBearingVariableInterestRate
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= eme_CreditAgreement2013MemberMember
/ us-gaap_VariableRateAxis
= us-gaap_PrimeRateMember
 
Prime Rate | Minimum | 2013 Credit Agreement        
Line of Credit Facility [Line Items]        
Basis spread on variable rate 0.25%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
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/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_VariableRateAxis
= us-gaap_PrimeRateMember
     
Prime Rate | Maximum | 2013 Credit Agreement        
Line of Credit Facility [Line Items]        
Basis spread on variable rate 0.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
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/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_VariableRateAxis
= us-gaap_PrimeRateMember
     
London Interbank Offered Rate (LIBOR) | 2013 Credit Agreement        
Line of Credit Facility [Line Items]        
Commercial lending rate 0.17%us-gaap_LongTermDebtPercentageBearingVariableInterestRate
/ us-gaap_DebtInstrumentAxis
= eme_CreditAgreement2013MemberMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
  0.17%us-gaap_LongTermDebtPercentageBearingVariableInterestRate
/ us-gaap_DebtInstrumentAxis
= eme_CreditAgreement2013MemberMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
 
London Interbank Offered Rate (LIBOR) | Minimum | 2013 Credit Agreement        
Line of Credit Facility [Line Items]        
Basis spread on variable rate 1.25%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
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/ us-gaap_RangeAxis
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/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
     
London Interbank Offered Rate (LIBOR) | Maximum | 2013 Credit Agreement        
Line of Credit Facility [Line Items]        
Basis spread on variable rate 1.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
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= eme_CreditAgreement2013MemberMember
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