Annual report pursuant to Section 13 and 15(d)

SHARE-BASED COMPENSATION Option Activity (Details)

v2.4.1.9
SHARE-BASED COMPENSATION Option Activity (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Non-vested Options    
Outstanding as of December 31, 2013 200,556era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsNonvestedNumberofShares  
Forfeited (in shares) 0era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedNumberofShares  
Outstanding as of December 31, 2014 77,500era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsNonvestedNumberofShares 200,556era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsNonvestedNumberofShares
Nonvested Options    
Outstanding as of December 31, 2013 $ 10.21era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue  
Granted $ 10.86us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue $ 9.59us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Vested $ 9.36era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue  
Forfeited $ 0.00era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsNonvestedOptionsForfeitedWeightedAverageGrantDateFairValue  
Outstanding as of December 31, 2014 $ 9.54era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue $ 10.21era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValue
Vested/Exercisable Options    
Outstanding as of December 31, 2013 127,484us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber  
Granted (in shares) 0era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedandExpectedtoVestGrantsinPeriodExercisableNumber  
Vested (in shares) 168,056era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedandExpectedtoVestVestedinPeriodExercisableNumber  
Exercised (in shares) (15,892)era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedandExpectedtoVestExercisesinPeriodExercisableNumber  
Expired (in shares) (15,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod  
Forfeited (in shares) 0era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedandExpectedtoVestForfeituresinPeriodExercisableNumber  
Outstanding as of December 31, 2014 264,648us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber 127,484us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber
Vested/Exercisable Options    
Outstanding as of December 31, 2013 $ 16.14us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice  
Granted $ 0.00era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedandExpectedtoVestGrantsinPeriodExercisableWeightedAverageExercisePrice  
Vested $ 22.02era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedandExpectedtoVestVestedinPeriodExercisableWeightedAverageExercisePrice  
Exercised $ 20.15era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedandExpectedtoVestExercisesinPeriodExercisableWeightedAverageExercisePrice  
Expired $ 26.23us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice  
Forfeited $ 0.00era_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedandExpectedtoVestForfeituresinPeriodExercisableWeightedAverageExercisePrice  
Outstanding as of December 31, 2014 $ 19.06us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice $ 16.14us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice
Total Options    
Outstanding as of December 31, 2013 328,040us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber  
Granted (in shares) 45,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross  
Exercised (in shares) (15,892)us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised  
Expired (in shares) (15,000)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod  
Forfeited (in shares) 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod  
Outstanding as of December 31, 2014 342,148us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber 328,040us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Total Options    
Outstanding as of December 31, 2013 $ 19.05us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice  
Granted $ 29.24us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice  
Exercised $ 20.15us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice  
Expired $ 26.23us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice  
Forfeited $ 0.00us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice  
Outstanding as of December 31, 2014 $ 20.02us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice $ 19.05us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice