| **Pension Plans And Other Postretirement Benefits (Components Of Net Periodic Benefit Costs) (Details) - USD ($) $ in Thousands** | 3 Months Ended | 6 Months Ended |
|-----------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| Pension Benefits [Member]                                                                                                         |           |           |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                  |           |           |   |   |
| Service cost                                                                                                                      | $ 794          | $ 784          | $ 1,587 | $ 1,610 |
| Interest cost                                                                                                                     | 3,108          | 3,251          | 6,217 | 6,536 |
| Expected return on plan assets                                                                                                    | (4,270)        | (4,215)        | (8,539) | (8,481) |
| Amortization of prior service cost                                                                                                | 145            | 145            | 290 | 290 |
| Amortization of actuarial loss                                                                                                    | 2,001          | 1,797          | 4,002 | 3,557 |
| Settlement charge                                                                                                                 |           |           |   | 3,028 |
| Special termination benefit charge                                                                                                |           |           |   | 302 |
| Net periodic benefit cost                                                                                                         | 1,778          | 1,762          | 3,557 | 6,842 |
| Other Postretirement Benefits [Member]                                                                                            |           |           |   |   |
| **Defined Benefit Plan Disclosure [Line Items]**                                                                                  |           |           |   |   |
| Service cost                                                                                                                      | 255            | 253            | 510 | 508 |
| Interest cost                                                                                                                     | 737            | 726            | 1,473 | 1,476 |
| Expected return on plan assets                                                                                                    | (647)          | (645)          | (1,294) | (1,356) |
| Amortization of prior service cost                                                                                                | (127)          | (137)          | (254) | (274) |
| Amortization of actuarial loss                                                                                                    | 291            | 220            | 583 | 487 |
| Net periodic benefit cost                                                                                                         | $ 509          | $ 417          | $ 1,018 | $ 841 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.
+ 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 (h)(5) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920
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| X                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
+ Details**Name:**us-gaap_DefinedBenefitPlanDisclosureLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.
+ 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 (h)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of cost recognized for passage of time related to defined benefit plan.
+ 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 (h)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of net periodic benefit cost (credit) for defined benefit plan.
+ 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 (h) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.
+ 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 (h)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920
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| X                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined benefit plan amortization of actuarial loss.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined benefit plan settlement charge.
+ References
No definition available.
+ Details**Name:**wtr_DefinedBenefitPlanSettlementCharge**Namespace Prefix:**wtr_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Defined Benefit Plan, Special Termination Benefit Charge
+ References
No definition available.
+ Details**Name:**wtr_DefinedBenefitPlanSpecialTerminationBenefitCharge**Namespace Prefix:**wtr_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |