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Retirement Plan (Details) (USD $) | 12 Months Ended
--- | ---
Jun. 30, 2013 | Jun. 30, 2012 | Jun. 30, 2011
Retirement Plan |  |  |
Employer match of employee contributions of first 6% of eligible compensation (as a percent) | 100.00% |  |
Percentage of eligible compensation, matched 100% by employer | 6.00% |  |
Matching contribution to the plan | $ 89,810 | $ 84,738 | $ 77,168

X
- Definition Represents the first level of employee contributions (percentage of compensation) which are matched by the employer. + References No definition available. + Details
Name: | epm_DefinedContributionPlanEmployerMatchEmployeeContributionLevelOne
Namespace Prefix: | epm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the employer matching contribution of the first level of employee contributions. + References No definition available. + Details
Name: | epm_DefinedContributionPlanEmployerMatchLevelOne
Namespace Prefix: | epm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_CompensationAndRetirementDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration