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Regulatory Assets and Liabilities (Details) - USD ($) | Dec. 31, 2019 | Dec. 31, 2018
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Regulatory Asset [Domain] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | $ 145,746,000 | $ 154,901,000
Asset Retirement Obligation [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 10,756,000 | 9,199,000
Debt Related Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 8,885,000 | 9,288,000
Deferred Pension And Other Postretirement Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 6,216,000 | 0
Derivatives [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 26,875,000 | 31,830,000
Leases |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 2,400,000 | 59,000
Tax Recovery AFUDC Equity [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 7,060,000 | 6,482,000
Unfunded Pension and Other Postretirement Plans Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 83,214,000 | 96,030,000
Other Regulatory Asset [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | $ 340,000 | $ 2,013,000

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- 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
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- Definition The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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