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Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Detail of regulatory liabilities |  |
Regulatory liabilities, current | $ 100,086 | $ 99,899
Regulatory liabilities, non-current | 2,452,536 | 948,916
Excess deferred income taxes - Tax Cuts and Jobs Act |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 0 | 0
Regulatory liabilities, non-current | 1,520,274 | 0
Asset retirement obligations |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 0 | 0
Regulatory liabilities, non-current | 332,171 | 279,976
Removal costs |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 18,238 | 29,899
Regulatory liabilities, non-current | 209,191 | 223,145
Other post retirement benefits |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 37,642 | 32,662
Regulatory liabilities, non-current | 151,985 | 123,913
Income taxes - deferred investment tax credit |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 2,164 | 4,368
Regulatory liabilities, non-current | 52,497 | 108,827
Income taxes - change in rates |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 2,573 | 1,771
Regulatory liabilities, non-current | 70,537 | 70,898
Spent nuclear fuel |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 6,924 | 0
Regulatory liabilities, non-current | 62,132 | 71,726
Renewable energy program |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 23,155 | 26,809
Regulatory liabilities, non-current | 0 | 0
Demand side management |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 3,066 | 0
Regulatory liabilities, non-current | 4,921 | 20,472
Sundance maintenance |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 0 | 0
Regulatory liabilities, non-current | 16,897 | 15,287
Deferred gains on utility property |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 4,423 | 2,063
Regulatory liabilities, non-current | 10,988 | 8,895
Four Corners coal reclamation |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 1,858 | 0
Regulatory liabilities, non-current | 18,921 | 18,248
Other |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 43 | 2,327
Regulatory liabilities, non-current | $ 2,022 | $ 7,529

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- Definition The amount for the individual regulatory current liability including deferred fuel and purchased power as itemized in a table of regulatory current liabilities as of the end of the period. + References No definition available. + Details
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- Definition The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.24) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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