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