Annual report pursuant to Section 13 and 15(d)

EARNINGS PER SHARE (Details)

v2.4.1.9
EARNINGS PER SHARE (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                      
Net Income Loss Available to Unvested Common Stockholders Basic                 $ 16,910us-gaap_UndistributedEarnings [1] $ 17,809us-gaap_UndistributedEarnings [1] $ (682)us-gaap_UndistributedEarnings [1]
Weighted average number of common shares outstanding—basic (in shares)                 20,073,378us-gaap_WeightedAverageNumberOfSharesOutstandingBasic 20,299,854us-gaap_WeightedAverageNumberOfSharesOutstandingBasic 24,500,000us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Weighted average number of common shares outstanding—diluted (in shares)                 20,139,581us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding 20,344,782us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding 24,500,000us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
Earnings Per Share, Basic (in usd per share) $ 0.16us-gaap_EarningsPerShareBasic $ 0.21us-gaap_EarningsPerShareBasic $ 0.26us-gaap_EarningsPerShareBasic $ 0.22us-gaap_EarningsPerShareBasic $ 0.09us-gaap_EarningsPerShareBasic $ 0.26us-gaap_EarningsPerShareBasic $ 0.25us-gaap_EarningsPerShareBasic $ 0.28us-gaap_EarningsPerShareBasic $ 0.84us-gaap_EarningsPerShareBasic $ 0.88us-gaap_EarningsPerShareBasic $ (0.03)us-gaap_EarningsPerShareBasic
Earnings Per Share, Diluted (in usd per share) $ 0.16us-gaap_EarningsPerShareDiluted $ 0.21us-gaap_EarningsPerShareDiluted $ 0.26us-gaap_EarningsPerShareDiluted $ 0.22us-gaap_EarningsPerShareDiluted $ 0.09us-gaap_EarningsPerShareDiluted $ 0.26us-gaap_EarningsPerShareDiluted $ 0.25us-gaap_EarningsPerShareDiluted $ 0.28us-gaap_EarningsPerShareDiluted $ 0.84us-gaap_EarningsPerShareDiluted $ 0.88us-gaap_EarningsPerShareDiluted $ (0.03)us-gaap_EarningsPerShareDiluted
Restricted Stock [Member]                      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                      
Net Income Loss Available to Unvested Common Stockholders Basic                 $ 207era_NetIncomeLossAvailabletoUnvestedCommonStockholdersBasic
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_RestrictedStockMember 		$ 175era_NetIncomeLossAvailabletoUnvestedCommonStockholdersBasic
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_RestrictedStockMember 		 
Series A Preferred Stock [Member]                      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                      
Assumed conversion of Series A Preferred Stock (in shares)                 0us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_SeriesAPreferredStockMember 		[2] 0us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_SeriesAPreferredStockMember 		[2] 0us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_SeriesAPreferredStockMember 		[2]
Antidilutive securities excluded from computation of earnings per share (in shares)                 0us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_SeriesAPreferredStockMember 		753,535us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_SeriesAPreferredStockMember 		7,679,623us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= us-gaap_SeriesAPreferredStockMember
Stock Options and Restricted Stock [Member]                      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                      
Net effect of dilutive stock options and restricted stock awards based on the treasury stock method (in shares)                 66,203us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= era_StockOptionsAndRestrictedStockMember 		[3] 44,928us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= era_StockOptionsAndRestrictedStockMember 		[3] 0us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= era_StockOptionsAndRestrictedStockMember 		[3]
Antidilutive securities excluded from computation of earnings per share (in shares)                 35,260us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= era_StockOptionsAndRestrictedStockMember 		7,973us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= era_StockOptionsAndRestrictedStockMember 		0us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= era_StockOptionsAndRestrictedStockMember
Restricted Stock [Member]                      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]                      
Shares of nonvested restricted stock 195,920us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember 		      264,760us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember 		      195,920us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember 		264,760us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember 		0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
[1] Excludes net income attributable to participating unvested restricted common shares of $207 and $175 for the years ended December 31, 2014 and 2013, respectively. No share awards existed in 2012.
[2] Excludes weighted average common shares of 0, 753,535 and 7,679,623 for the years ended December 31, 2014, 2013 and 2012, respectively, that were issuable upon the conversion of Series A preferred stock as the effect of their inclusion in the computation would have been antidilutive (see Note 9).
[3] Excludes weighted average common shares of 35,260 and 7,973 for the years ended December 31, 2014 and 2013, respectively, for certain share awards as the effect of their inclusion would have been antidilutive. No share awards existed in 2012.