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Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Thousands | Mar. 31, 2019 | Dec. 31, 2018
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Detail of regulatory liabilities |  |
Regulatory liabilities, current | $ 260,404 | $ 165,876
Regulatory liabilities, non-current | 2,272,082 | 2,325,976
Asset retirement obligations |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 0 | 0
Regulatory liabilities, non-current | 337,844 | 278,585
Removal costs |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 50,701 | 39,866
Regulatory liabilities, non-current | 156,578 | 177,533
Other postretirement benefits |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 37,864 | 37,864
Regulatory liabilities, non-current | 116,478 | 125,903
Income taxes — deferred investment tax credit |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 2,164 | 2,164
Regulatory liabilities, non-current | 51,027 | 51,120
Income taxes — change in rates |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 2,764 | 2,769
Regulatory liabilities, non-current | 69,954 | 70,069
Spent nuclear fuel |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 7,190 | 6,503
Regulatory liabilities, non-current | 54,866 | 57,002
Renewable energy standard |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 47,943 | 44,966
Regulatory liabilities, non-current | 0 | 20
Demand side management |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 1,581 | 14,604
Regulatory liabilities, non-current | 24,146 | 4,123
Sundance maintenance |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 6,657 | 1,278
Regulatory liabilities, non-current | 11,637 | 17,228
Deferred gains on utility property |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 3,923 | 4,423
Regulatory liabilities, non-current | 5,975 | 6,581
Four Corners coal reclamation |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 1,858 | 1,858
Regulatory liabilities, non-current | 17,690 | 17,871
Tax expense adjustor mechanism |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 14 | 3,237
Regulatory liabilities, non-current | 0 | 0
Other |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 42 | 42
Regulatory liabilities, non-current | 4,253 | 3,541
ACC | Excess deferred income taxes - ACC - Tax Cuts and Jobs Act |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 91,401 | 0
Regulatory liabilities, non-current | 1,178,216 | 1,272,709
United States Federal Energy Regulatory Commission | Excess deferred income taxes - ACC - Tax Cuts and Jobs Act |  |
Detail of regulatory liabilities |  |
Regulatory liabilities, current | 6,302 | 6,302
Regulatory liabilities, non-current | $ 243,418 | $ 243,691

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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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