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Pension Plans And Other Postretirement Benefit Plans (Change in Benefit Obligation and Plan Assets) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items] |  |  |
Liability, Defined Benefit Plan, Current | $ (8,826) | $ (9,151) |
Liability, Defined Benefit Plan, Noncurrent | (212,006) | (222,537) |
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax | (10,259) | (7,866) |
Pension Plan And SERP [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Benefit obligation as of beginning of year | 671,629 | 716,561 |
Service cost | 19,755 | 21,614 | $ 20,406
Interest cost | 28,417 | 26,096 | 27,898
Actuarial (gain)/loss | 57,829 | (48,641) |
Benefits paid | (35,248) | (44,001) |
Benefit obligation as of end of year | 742,382 | 671,629 | 716,561
Fair value of plan assets as of beginning of year | 544,051 | 605,652 |
Actual return on plan assets | 109,942 | (40,954) |
Employer contributions | 22,000 | 22,000 |
Benefits Paid | (33,930) | (42,647) |
Fair value of plan assets as of end of year | 642,063 | 544,051 | 605,652
Funded status | (100,319) | (127,578) |
Liability, Defined Benefit Plan, Current | (1,602) | (1,477) |
Liability, Defined Benefit Plan, Noncurrent | (98,717) | (126,101) |
Liability, Defined Benefit Plan | (100,319) | (127,578) |
Accumulated pension benefit obligation | 644,004 | 586,398 |
Unrecognized prior service cost | 2,105 | 2,308 |
Unrecognized net actuarial loss | 114,368 | 138,516 |
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Before Regulatory Asset, Net of Tax | 116,473 | 140,824 |
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax | 9,078 | 7,587 |
Less regulatory asset | $ (107,395) | $ (133,237) |
Discount rate for benefit obligation | 3.85% | 4.31% |
Discount rate for annual expense | 4.31% | 3.71% |
Expected long-term return on plan assets | 5.90% | 5.50% |
Rate of compensation increase | 4.66% | 4.67% |
Expected return on plan assets | $ (31,763) | $ (33,018) | (31,626)
Other Postretirement Benefits [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Benefit obligation as of beginning of year | 134,053 | 132,947 |
Service cost | 3,006 | 3,188 | 3,220
Interest cost | 5,598 | 4,831 | 5,490
Actuarial (gain)/loss | 23,344 | (610) |
Benefits paid | (6,705) | (6,303) |
Benefit obligation as of end of year | 159,296 | 134,053 | 132,947
Fair value of plan assets as of beginning of year | 36,852 | 37,953 |
Actual return on plan assets | 8,001 | (1,101) |
Employer contributions | 0 | 0 |
Benefits Paid | 0 | 0 |
Fair value of plan assets as of end of year | 44,853 | 36,852 | 37,953
Funded status | (114,443) | (97,201) |
Liability, Defined Benefit Plan, Current | (640) | (580) |
Liability, Defined Benefit Plan, Noncurrent | (113,803) | (96,621) |
Liability, Defined Benefit Plan | (114,443) | (97,201) |
Accumulated pension benefit obligation | 0 | 0 |
Unrecognized prior service cost | (4,400) | (5,230) |
Unrecognized net actuarial loss | 63,101 | 52,441 |
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Before Regulatory Asset, Net of Tax | 58,701 | 47,211 |
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax | 1,181 | 279 |
Less regulatory asset | $ (57,520) | $ (46,932) |
Discount rate for benefit obligation | 3.89% | 4.32% |
Discount rate for annual expense | 4.32% | 3.72% |
Expected long-term return on plan assets | 5.70% | 5.20% |
Expected return on plan assets | $ (2,101) | $ (1,973) | $ (1,899)
Other Postretirement Benefits [Member] | Pre-Age 65 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Medical cost trend - initial | 5.75% | 6.00% |
Medical cost trend - ultimate | 5.00% | 5.00% |
Ultimate medical cost trend year | 2023 | 2023 |
Other Postretirement Benefits [Member] | Post-Age 65 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Medical cost trend - initial | 6.50% | 6.25% |
Medical cost trend - ultimate | 5.00% | 5.00% |
Ultimate medical cost trend year | 2026 | 2024 |
Retirees [Member] | Other Postretirement Benefits [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Benefit obligation as of beginning of year | $ 63,796 |  |
Benefit obligation as of end of year | 72,816 | $ 63,796 |
Fully eligible employees [Member] | Other Postretirement Benefits [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Benefit obligation as of beginning of year | 29,902 |  |
Benefit obligation as of end of year | 34,545 | 29,902 |
Other participants [Member] | Other Postretirement Benefits [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Benefit obligation as of beginning of year | 40,355 |  |
Benefit obligation as of end of year | $ 51,935 | $ 40,355 |

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- Definition Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669686-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669646-108580 + Details
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- Definition Amount, after tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669686-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Amount, after tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=118930883&loc=SL7669686-108580 + Details
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- Definition Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 + Details
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- Definition Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(6) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964 + Details
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- 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/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 + Details
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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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