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Property, Plant, and Equipment (Details) - USD ($) $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 8,300,770 | $ 7,908,628 |
Less accumulated depreciation, depletion and amortization | 3,133,831 | 2,991,486 | $ 2,818,644
Net property, plant and equipment | 5,166,939 | 4,917,142 | 4,578,677
Electric |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | 2,323,403 | 2,227,145 | 2,148,569
Natural gas distribution |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | 2,868,853 | 2,688,123 | 2,499,093
Pipeline |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | 821,697 | 834,215 | 764,959
Construction materials and contracting |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | 2,028,476 | 1,910,562 | 1,768,006
Construction services |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | 220,796 | 213,370 | 188,586
Other |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | 37,545 | 35,213 | $ 28,108
Regulated Operation | Electric | Electric Generation Equipment |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 1,133,390 | 1,139,059 |
Weighted average depreciable life in years | 48 years |  |
Regulated Operation | Electric | Electric Distribution |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 464,442 | 443,780 |
Weighted average depreciable life in years | 46 years |  |
Regulated Operation | Electric | Electric Transmission |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 524,155 | 445,485 |
Weighted average depreciable life in years | 64 years |  |
Regulated Operation | Electric | Construction in Progress |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 61,766 | 66,664 |
Regulated Operation | Electric | Other Capitalized Property Plant and Equipment |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 139,650 | 132,157 |
Weighted average depreciable life in years | 14 years |  |
Regulated Operation | Natural gas distribution | Construction in Progress |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 16,836 | 39,506 |
Regulated Operation | Natural gas distribution | Other Capitalized Property Plant and Equipment |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 213,976 | 188,037 |
Weighted average depreciable life in years | 16 years |  |
Regulated Operation | Natural gas distribution | Gas Distribution [Member] |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 2,302,121 | 2,133,249 |
Weighted average depreciable life in years | 47 years |  |
Regulated Operation | Natural gas distribution | Gas Transmission [Member] |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 104,695 | 104,401 |
Weighted average depreciable life in years | 51 years |  |
Regulated Operation | Natural gas distribution | Natural gas storage |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 33,014 | 31,484 |
Weighted average depreciable life in years | 24 years |  |
Regulated Operation | Natural gas distribution | General |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 198,211 | 191,446 |
Weighted average depreciable life in years | 14 years |  |
Regulated Operation | Pipeline | Construction in Progress |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 46,690 | 22,597 |
Regulated Operation | Pipeline | Other Capitalized Property Plant and Equipment |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 49,640 | 48,340 |
Weighted average depreciable life in years | 17 years |  |
Regulated Operation | Pipeline | Gas Transmission [Member] |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 665,567 | 636,796 |
Weighted average depreciable life in years | 46 years |  |
Regulated Operation | Pipeline | Gathering |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 0 | 35,661 |
Regulated Operation | Pipeline | Gas Storage [Member] |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 52,632 | 50,001 |
Weighted average depreciable life in years | 53 years |  |
Unregulated Operation | Pipeline | Construction in Progress |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 4 | 154 |
Unregulated Operation | Pipeline | Other Capitalized Property Plant and Equipment |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 7,164 | 9,518 |
Weighted average depreciable life in years | 11 years |  |
Unregulated Operation | Pipeline | Gathering and processing |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 0 | 31,148 |
Unregulated Operation | Construction materials and contracting | Construction in Progress |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | 23,803 | 25,018 |
Unregulated Operation | Construction materials and contracting | Land [Member] |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | 132,948 | 127,729 |
Unregulated Operation | Construction materials and contracting | Building and Building Improvements [Member] |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 130,417 | 122,064 |
Weighted average depreciable life in years | 21 years |  |
Unregulated Operation | Construction materials and contracting | Machinery and Equipment [Member] |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 1,284,604 | 1,180,343 |
Weighted average depreciable life in years | 12 years |  |
Unregulated Operation | Construction materials and contracting | Aggregate reserves [Member] |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 456,704 | 455,408 |
Unregulated Operation | Construction services | Other Capitalized Property Plant and Equipment |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 8,824 | 17,952 |
Weighted average depreciable life in years | 4 years |  |
Unregulated Operation | Construction services | Land [Member] |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 7,218 | 7,146 |
Unregulated Operation | Construction services | Building and Building Improvements [Member] |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 41,674 | 31,735 |
Weighted average depreciable life in years | 25 years |  |
Unregulated Operation | Construction services | Machinery and Equipment [Member] |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 163,080 | 156,537 |
Weighted average depreciable life in years | 7 years |  |
Unregulated Operation | Other | Other Capitalized Property Plant and Equipment |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 34,897 | 32,565 |
Weighted average depreciable life in years | 12 years |  |
Unregulated Operation | Other | Land [Member] |  |  |
Property, plant and equipment [Line Items] |  |  |
Property, Plant and Equipment, Gross | $ 2,648 | $ 2,648 |

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