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Pension Plans and Other Postretirement Benefit Plans - Additional Information (Details) - USD ($) $ in Thousands | 6 Months Ended
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Jun. 30, 2020 | Jun. 30, 2019
Defined Benefit Plan Disclosure [Line Items] |  |
Payment for pension benefits | $ 14,600 | $ 14,600
Percentage of service related net periodic benefit costs capitalized to utility property | 40.00% |
Percentage of service related net periodic benefit costs recorded to operating expenses | 60.00% |
Percentage of non-service related net periodic benefit costs capitalized to regulatory assets | 40.00% |
Percentage of non-service related net periodic benefit costs recorded to other expense | 60.00% |
Pension Plans, Defined Benefit [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Defined benefit plan, expected future employer contributions, next fiscal year | $ 22,000 |

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- Definition Percentage of non-service related net periodic benefit costs recorded to other expense. + References No definition available. + Details
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- Definition Percentage of service related net periodic benefit costs recorded to operating expenses. + References No definition available. + Details
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- Definition Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year. + 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 (g) -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 18 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4587-114921 + Details
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- Definition Amount of cash outflow for pension benefit. Includes, but is not limited to, employer contribution to fund plan asset and payment to retiree. Excludes other postretirement benefit. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3536-108585 + Details
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- Details
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