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Select Balance Sheet Information - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Property, Plant and Equipment [Line Items] |  |
Property, Plant and Equipment, net of accumulated depreciation | $ 2,060,792 | $ 2,049,273
Electric Plant in Service |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 2,760,560 | 2,734,430
Less Accumulated Depreciation and Amortization | 796,161 | 778,988
Property, Plant and Equipment, net of accumulated depreciation | 1,964,399 | 1,955,442
Nonelectric Property, Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 272,061 | 268,020
Less Accumulated Depreciation and Amortization | 175,668 | 174,189
Property, Plant and Equipment, net of accumulated depreciation | 96,393 | 93,831
Electric Plant in Service | Electric Plant in Service |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 2,682,884 | 2,531,352
Construction Work in Progress | Electric Plant in Service |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 77,676 | 203,078
Construction Work in Progress | Nonelectric Property, Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | 12,086 | 9,290
Nonelectric Property, Plant and Equipment in Service | Nonelectric Property, Plant and Equipment |  |
Property, Plant and Equipment [Line Items] |  |
Property, plant and equipment, gross | $ 259,975 | $ 258,730

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- Definition Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.13) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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