Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments (Narrative) (Details)

v2.4.1.9
Derivative Instruments (Narrative) (Details) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Dec. 31, 2011
interest_rate_derivative_held
Derivative [Line Items]        
Derivative Liability $ 200,000us-gaap_DerivativeLiabilities   $ 300,000us-gaap_DerivativeLiabilities  
Recognized gain 100,000us-gaap_DerivativeGainOnDerivative 100,000us-gaap_DerivativeGainOnDerivative    
Derivative Loss 300,000us-gaap_DerivativeLossOnDerivative      
Interest Rate Swap [Member]        
Derivative [Line Items]        
Number of interest rate swaps held       2us-gaap_NumberOfInterestRateDerivativesHeld
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
Notional amount of interest rate derivatives       $ 27,100,000us-gaap_DerivativeAssetNotionalAmount
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
Interest Rate Swap Agreement 1 [Member] | Interest Rate Swap [Member]        
Derivative [Line Items]        
Fixed interest rate       1.29%us-gaap_DerivativeFixedInterestRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ era_InterestRateSwapAgreementAxis
= era_InterestRateSwapAgreement1Member
Interest Rate Swap Agreement 2 [Member] | Interest Rate Swap [Member]        
Derivative [Line Items]        
Fixed interest rate       1.76%us-gaap_DerivativeFixedInterestRate
/ us-gaap_DerivativeInstrumentRiskAxis
= us-gaap_InterestRateSwapMember
/ era_InterestRateSwapAgreementAxis
= era_InterestRateSwapAgreement2Member