Revenue from contracts with customers - Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 1,204,349	$ 1,422,882
Other revenues	9,476	7,216
Total external operating revenues	1,213,825	1,430,098
Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(31,899)	(27,939)
Total external operating revenues	(31,899)	(27,939)
Operating Segments
Disaggregation of Revenue [Line Items]
Total external operating revenues	1,244,291	1,456,465
Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	58,228	48,487
Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,382	3,861
Electrical & mechanical specialty contracting
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	439,378	590,263
Transmission & distribution specialty contracting
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	176,860	152,022
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	22,566	20,063
Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	302,325	365,476
Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	203,645	241,274
Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	25,928	27,601
Other utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,936	1,774
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(28)	(27)
Electric | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	109,624	98,560
Other revenues	(1,897)	(2,863)
Total external operating revenues	107,727	95,697
Electric | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Electric | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Electric | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Electric | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Electric | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	15,630	11,878
Electric | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	39,222	37,825
Electric | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	41,515	36,347
Electric | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,349	10,763
Electric | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,936	1,774
Natural gas distribution | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(56)	(70)
Natural gas distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	457,548	567,571
Other revenues	1,921	(1,974)
Total external operating revenues	459,469	565,597
Natural gas distribution | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	14,591	13,504
Natural gas distribution | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Natural gas distribution | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Natural gas distribution | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Natural gas distribution | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,201	4,721
Natural gas distribution | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	263,103	327,651
Natural gas distribution | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	162,130	204,927
Natural gas distribution | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	14,579	16,838
Natural gas distribution | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Pipeline | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(30,311)	(26,270)
Pipeline | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	20,964	14,433
Other revenues	47	38
Total external operating revenues	21,011	14,471
Pipeline | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	43,637	34,983
Pipeline | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,382	3,861
Pipeline | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Pipeline | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Pipeline | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,256	1,859
Pipeline | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Pipeline | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Pipeline | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Pipeline | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Construction services | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(87)	0
Construction services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	616,197	742,318
Other revenues	9,405	12,015
Total external operating revenues	625,602	754,333
Construction services | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Construction services | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Construction services | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	439,378	590,263
Construction services | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	176,860	152,022
Construction services | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	46	33
Construction services | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Construction services | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Construction services | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Construction services | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(1,417)	(1,572)
Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16	0
Other revenues	0	0
Total external operating revenues	16	0
Other | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,433	1,572
Other | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0
Other | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 0	$ 0