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Summary of Significant Accounting Policies - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Utility Plant and Depreciation [Line Items] |  |  |
Depreciation and amortization | $ 582,354 | $ 534,118 | $ 485,829
Net | 12,370,614 | 11,669,526 |
Construction work in progress | 1,170,062 | 1,291,498 |
Palo Verde sale leaseback, net of accumulated depreciation | 105,775 | 109,645 |
Intangible assets, net of accumulated amortization | 262,902 | 257,189 |
Nuclear fuel, net of accumulated amortization | 120,217 | 117,408 |
Total property, plant and equipment | 14,029,570 | 13,445,266 |
Electric Service |  |  |
Utility Plant and Depreciation [Line Items] |  |  |
Generation | 8,285,514 | 7,963,998 |
Transmission | 3,033,579 | 2,836,578 |
Distribution | 6,378,345 | 6,025,856 |
General plant | 1,039,190 | 971,629 |
Plant in service and held for future use | 18,736,628 | 17,798,061 |
Accumulated depreciation and amortization | (6,366,014) | (6,128,535) |
Net | 12,370,614 | 11,669,526 |
Construction work in progress | 1,170,062 | 1,291,498 |
Palo Verde sale leaseback, net of accumulated depreciation | 105,775 | 109,645 |
Intangible assets, net of accumulated amortization | 262,902 | 257,189 |
Nuclear fuel, net of accumulated amortization | 120,217 | 117,408 |
Total property, plant and equipment | $ 14,029,570 | $ 13,445,266 |

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