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Regulatory Matters - Schedule of Regulatory Liabilities (Details) - USD ($) $ in Thousands | Sep. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Detail of regulatory liabilities |  |
Current | $ 308,019 | $ 234,912
Non-Current | 2,079,323 | 2,267,835
Asset retirement obligations |  |
Detail of regulatory liabilities |  |
Current | 0 | 0
Non-Current | 442,035 | 418,423
Removal costs |  |
Detail of regulatory liabilities |  |
Current | 51,519 | 47,356
Non-Current | 112,168 | 136,072
Other postretirement benefits |  |
Detail of regulatory liabilities |  |
Current | 37,575 | 37,575
Non-Current | 109,035 | 139,634
Four Corners coal reclamation |  |
Detail of regulatory liabilities |  |
Current | 5,461 | 1,059
Non-Current | 49,151 | 51,704
Spent nuclear fuel |  |
Detail of regulatory liabilities |  |
Current | 6,520 | 6,676
Non-Current | 46,526 | 51,019
Income taxes — change in rates |  |
Detail of regulatory liabilities |  |
Current | 2,802 | 2,797
Non-Current | 48,541 | 68,265
Income taxes — deferred investment tax credit |  |
Detail of regulatory liabilities |  |
Current | 2,199 | 2,202
Non-Current | 47,765 | 50,034
Renewable energy standard |  |
Detail of regulatory liabilities |  |
Current | 35,813 | 39,287
Non-Current | 1,128 | 10,300
Sundance maintenance |  |
Detail of regulatory liabilities |  |
Current | 2,200 | 5,698
Non-Current | 12,303 | 11,319
Demand side management |  |
Detail of regulatory liabilities |  |
Current | 17,394 | 15,024
Non-Current | 0 | 24,146
Property tax deferral |  |
Detail of regulatory liabilities |  |
Current | 0 | 0
Non-Current | 11,784 | 7,046
Deferred fuel and purchased power — mark-to-market (Note 7) |  |
Detail of regulatory liabilities |  |
Current | 10,894 | 0
Non-Current | 0 | 0
FERC transmission true up |  |
Detail of regulatory liabilities |  |
Current | 5,965 | 1,045
Non-Current | 4,291 | 2,004
Active union medical trust |  |
Detail of regulatory liabilities |  |
Current | 0 | 0
Non-Current | 6,993 | 2,041
Tax expense adjustor mechanism |  |
Detail of regulatory liabilities |  |
Current | 6,542 | 7,018
Non-Current | 0 | 0
Deferred gains on utility property |  |
Detail of regulatory liabilities |  |
Current | 2,423 | 2,423
Non-Current | 2,379 | 4,163
TCA balancing account |  |
Detail of regulatory liabilities |  |
Current | 0 | 0
Non-Current | 2,665 | 0
Other |  |
Detail of regulatory liabilities |  |
Current | 250 | 532
Non-Current | 275 | 255
ACC | Excess deferred income taxes - ACC - Tax Cuts and Jobs Act |  |
Detail of regulatory liabilities |  |
Current | 113,206 | 59,918
Non-Current | 952,531 | 1,054,053
United States Federal Energy Regulatory Commission | Excess deferred income taxes - ACC - Tax Cuts and Jobs Act |  |
Detail of regulatory liabilities |  |
Current | 7,256 | 6,302
Non-Current | $ 229,753 | $ 237,357

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