Annual report pursuant to Section 13 and 15(d)

DERIVATIVE INSTRUMENTS Narrative (Details)

v2.4.1.9
DERIVATIVE INSTRUMENTS Narrative (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
interest_rate_derivative_held
Derivative [Line Items]        
Fair value of derivative liabilities $ 300,000us-gaap_DerivativeLiabilities $ 600,000us-gaap_DerivativeLiabilities    
Recognized gain 300,000us-gaap_DerivativeGainOnDerivative 400,000us-gaap_DerivativeGainOnDerivative    
Derivative loss 800,000us-gaap_DerivativeLossOnDerivative   500,000us-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       $ 27,500,000invest_DerivativeNotionalAmount
/ 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