| **Pension Plans And Other Post-Retirement Benefits (Schedule Of Accumulated And Projected Benefit Obligations) (Details) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2014                                                                                                                                                                                                                        | Dec. 31, 2013                                                                                                                                                                                                                        |
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| Projected Benefit [Member]                                                                                                                                                 |                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                 |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                                           |                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                 |
| Projected benefit obligation                                                                                                                                               | $ 311,609us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= wtr_ProjectedBenefitMember   | $ 281,161us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateProjectedBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= wtr_ProjectedBenefitMember   |
| Fair value of plan assets                                                                                                                                                  | 244,897us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= wtr_ProjectedBenefitMember          | 232,347us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= wtr_ProjectedBenefitMember          |
| Accumulated Benefit [Member]                                                                                                                                               |                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                 |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                                                           |                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                 |
| Accumulated benefit obligation                                                                                                                                             | 293,364us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateAccumulatedBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= wtr_AccumulatedBenefitMember | 246,843us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateAccumulatedBenefitObligation/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= wtr_AccumulatedBenefitMember |
| Fair value of plan assets                                                                                                                                                  | $ 244,897us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= wtr_AccumulatedBenefitMember      | $ 232,347us-gaap_DefinedBenefitPlanPensionPlansWithAccumulatedBenefitObligationsInExcessOfPlanAssetsAggregateFairValueOfPlanAssets/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis= wtr_AccumulatedBenefitMember      |

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| - Definition
If aggregate disclosures are presented, the aggregate pension accumulated benefit obligation for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=34716465&loc=d3e4179-114921Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2417-114920
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| - Definition
If aggregate disclosures are presented, the aggregate fair value of plan assets for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=34716465&loc=d3e4179-114921Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2417-114920
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| - Definition
If aggregate disclosures are presented, the aggregate projected benefit obligation for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=34716465&loc=d3e4179-114921Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2417-114920
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