Annual report pursuant to Section 13 and 15(d)

Schedule of Equity Method Investment, Financial Information, Statement of Operations (Details)

v2.4.1.9
Schedule of Equity Method Investment, Financial Information, Statement of Operations (Details) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]      
Equity Method Investment Summarized Financial Information, Equity $ 2,900,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationEquity $ 4,600,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationEquity  
Other Investments [Member]      
Schedule of Equity Method Investments [Line Items]      
Operating revenues 2,737,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember 		4,682,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember 		20,009,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember
Operating and administrative 750,000era_EquityMethodInvestmentSummarizedFinancialInformationOperatingAndAdministrativeExpense
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember 		1,035,000era_EquityMethodInvestmentSummarizedFinancialInformationOperatingAndAdministrativeExpense
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember 		16,221,000era_EquityMethodInvestmentSummarizedFinancialInformationOperatingAndAdministrativeExpense
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember
Depreciation and amortization 2,370,000era_EquityMethodInvestmentSummarizedFinancialInformationDepreciation
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember 		3,450,000era_EquityMethodInvestmentSummarizedFinancialInformationDepreciation
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember 		3,165,000era_EquityMethodInvestmentSummarizedFinancialInformationDepreciation
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember
Total Costs and Expenses 3,120,000era_EquityMethodInvestmentSummarizedFinancialInformationCostsAndExpenses
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember 		4,485,000era_EquityMethodInvestmentSummarizedFinancialInformationCostsAndExpenses
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember 		19,386,000era_EquityMethodInvestmentSummarizedFinancialInformationCostsAndExpenses
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember
Operating income (383,000)us-gaap_EquityMethodInvestmentSummarizedFinancialInformationIncomeLossFromContinuingOperationsBeforeExtraordinaryItems
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember 		197,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationIncomeLossFromContinuingOperationsBeforeExtraordinaryItems
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember 		623,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationIncomeLossFromContinuingOperationsBeforeExtraordinaryItems
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember
Net income (749,000)us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember 		(476,000)us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember 		540,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_OtherInvestmentsMember
Dart Holding Company Ltd. [Member]      
Schedule of Equity Method Investments [Line Items]      
Operating revenues 40,174,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember 		39,185,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember 		42,870,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember
Operating and administrative 31,755,000era_EquityMethodInvestmentSummarizedFinancialInformationOperatingAndAdministrativeExpense
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember 		31,538,000era_EquityMethodInvestmentSummarizedFinancialInformationOperatingAndAdministrativeExpense
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember 		33,706,000era_EquityMethodInvestmentSummarizedFinancialInformationOperatingAndAdministrativeExpense
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember
Depreciation and amortization 4,129,000era_EquityMethodInvestmentSummarizedFinancialInformationDepreciation
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember 		5,213,000era_EquityMethodInvestmentSummarizedFinancialInformationDepreciation
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember 		5,375,000era_EquityMethodInvestmentSummarizedFinancialInformationDepreciation
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember
Total Costs and Expenses 35,884,000era_EquityMethodInvestmentSummarizedFinancialInformationCostsAndExpenses
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember 		36,751,000era_EquityMethodInvestmentSummarizedFinancialInformationCostsAndExpenses
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember 		39,081,000era_EquityMethodInvestmentSummarizedFinancialInformationCostsAndExpenses
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember
Operating income 4,290,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationIncomeLossFromContinuingOperationsBeforeExtraordinaryItems
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember 		2,434,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationIncomeLossFromContinuingOperationsBeforeExtraordinaryItems
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember 		3,789,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationIncomeLossFromContinuingOperationsBeforeExtraordinaryItems
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember
Net income $ 2,172,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember 		$ 789,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember 		$ 1,245,000us-gaap_EquityMethodInvestmentSummarizedFinancialInformationNetIncomeLoss
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= era_DartHoldingCompanyLtdMember