Annual report pursuant to Section 13 and 15(d)

SHARE-BASED COMPENSATION Schedule of Stock Options Valuation Assumptions (Details)

v2.4.1.9
SHARE-BASED COMPENSATION Schedule of Stock Options Valuation Assumptions (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]    
Risk free interest rate 1.75%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate 0.81%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
Expected life (years) 5 years 5 years
Volatility 39.62%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate 50.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
Dividend yield 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
Weighted average exercise price of options granted (per option) $ 29.24us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice $ 19.05us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice
Fair value of stock options granted $ 10.86era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsGrantsinPeriodWeightedAverageGrantDateFairValueIncludingConvertedInstruments $ 7.87era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsGrantsinPeriodWeightedAverageGrantDateFairValueIncludingConvertedInstruments