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Benefit Plans Components of Benefit Plans (Details) (USD $) | 0 Months Ended | 9 Months Ended
--- | --- | ---
Jun. 30, 2014 | Jun. 30, 2014 plans
Defined Benefit Plan Disclosure |  |
Number of defined benefit plans |  | 1
Number of defined contribution plans |  | 1
Number of unfunded post-retirement health care plans |  | 2
Defined Contribution Plan, Automatic Employer Contribution | 4.50% |
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent | $ 0.75 |
Maximum |  |
Defined Benefit Plan Disclosure |  |
Defined Contribution Plan, Employer Matching Contribution, Percent of Match | 4.50% |

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- Definition Automatic, non-elective percentage of base compensation that employer contributes to participants account in the defined contribution plan only. + References No definition available. + Details
Name: | tve_DefinedContributionPlanAutomaticEmployerContribution
Namespace Prefix: | tve_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount per dollar that an employer matches employee contributions to a defined contribution plan. + References No definition available. + Details
Name: | tve_DefinedContributionPlanEmployerMatchingContributionRate
Namespace Prefix: | tve_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

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- Definition The number of qualified defined benefit pension plans. + References No definition available. + Details
Name: | tve_NumberOfQualifiedDefinedBenefitPlans
Namespace Prefix: | tve_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition The number of qualified defined contribution pension plans. + References No definition available. + Details
Name: | tve_NumberOfQualifiedDefinedContributionPlans
Namespace Prefix: | tve_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition The number of unfunded post-retirement health care plans that provide for non-vested contributions toward the cost of certain retirees' medical coverage. + References No definition available. + Details
Name: | tve_NumberOfUnfundedPostRetirementHealthCarePlans
Namespace Prefix: | tve_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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

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- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration