| **Pension Plans And Other Post-Retirement Benefits (Schedule Of Net Periodic Benefit Cost Not Yet Recognized) (Details) - USD ($) $ in Thousands** | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 |
|----------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|
| Pension Benefits [Member]                                                                                                                          |          |          |          |
| Net actuarial loss                                                                                                                                 |          | $ 92,436      | $ 87,930      |
| Prior service cost (credit)                                                                                                                        |          | 3,841         | 4,419         |
| Total recognized in regulatory assets                                                                                                              |          | 96,277        | 92,349        |
| Other Postretirement Benefits [Member]                                                                                                             |          |          |          |
| Net actuarial loss                                                                                                                                 |          | 15,441        | 14,469        |
| Prior service cost (credit)                                                                                                                        |          | (2,378)       | (2,926)       |
| Total recognized in regulatory assets                                                                                                              |          | $ 13,063      | $ 11,543      |
| Scenario, Forecast [Member] | Pension Benefits [Member]                                                                                            |          |          |          |
| Net actuarial loss                                                                                                                                 | $ 8,023       |          |          |
| Prior service cost (credit)                                                                                                                        | 579           |          |          |
| Scenario, Forecast [Member] | Other Postretirement Benefits [Member]                                                                               |          |          |          |
| Net actuarial loss                                                                                                                                 | 1,165         |          |          |
| Prior service cost (credit)                                                                                                                        | $ (509)       |          |          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The pretax total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580
+ Details**Name:**us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Prior Service Cost -URI http://asc.fasb.org/extlink&oid=49177896Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580
+ Details**Name:**us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined Benefit Plan Actuarial Gain Loss, Not Included In Periodic Benefit Cost
+ References
No definition available.
+ Details**Name:**wtr_DefinedBenefitPlanActuarialGainLossNotIncludedInPeriodicBenefitCost**Namespace Prefix:**wtr_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_PensionPlansDefinedBenefitMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |