Revenue from contracts with customers - Schedule of Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 1,041,392	$ 991,276	$ 3,281,504	$ 3,493,191
Other revenues	9,124	9,519	30,382	28,829
Total external operating revenues	1,050,516	1,000,795	3,311,886	3,522,020
Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(5,563)	(5,486)	(48,294)	(44,591)
Total external operating revenues	(5,563)	(5,486)	(48,294)	(44,591)
Operating Segments
Disaggregation of Revenue [Line Items]
Total external operating revenues	1,054,646	1,004,592	3,355,897	3,560,199
Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	57,215	48,388	172,173	142,941
Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	6,053	4,808	16,766	12,427
Electrical & mechanical specialty contracting
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	534,613	514,378	1,476,006	1,672,948
Transmission & distribution specialty contracting
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	216,062	192,056	583,803	511,563
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	31,057	24,098	78,149	66,231
Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	99,004	103,036	539,456	620,304
Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	84,335	90,114	393,874	440,846
Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,571	18,019	63,525	65,173
Other utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,045	1,865	6,046	5,349
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(96)	(27)	(188)	(82)
Electric | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	111,557	111,343	321,183	302,574
Other revenues	(3,173)	(3,254)	(5,915)	(7,799)
Total external operating revenues	108,384	108,089	315,268	294,775
Electric | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Electric | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Electric | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Electric | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Electric | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	16,182	14,701	44,998	38,111
Electric | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	37,076	34,303	107,735	102,953
Electric | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	46,648	49,754	129,783	124,363
Electric | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,702	10,747	32,809	31,880
Electric | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	2,045	1,865	6,046	5,349
Natural gas distribution | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(104)	(69)	(209)	(208)
Natural gas distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	131,395	133,227	788,218	917,018
Other revenues	2,122	1,669	6,200	2,469
Total external operating revenues	133,517	134,896	794,418	919,487
Natural gas distribution | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	15,279	13,050	43,194	38,225
Natural gas distribution | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Natural gas distribution | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Natural gas distribution | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Natural gas distribution | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,736	3,881	18,705	11,874
Natural gas distribution | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	61,928	68,733	431,721	517,351
Natural gas distribution | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	37,687	40,360	264,091	316,483
Natural gas distribution | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	6,869	7,272	30,716	33,293
Natural gas distribution | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(3,931)	(3,701)	(43,296)	(37,889)
Pipeline | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	47,595	40,361	112,352	88,967
Other revenues	33	43	119	119
Total external operating revenues	47,628	40,404	112,471	89,086
Pipeline | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	41,936	35,338	128,979	104,716
Pipeline | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	6,053	4,808	16,766	12,427
Pipeline | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	3,537	3,916	9,903	9,713
Pipeline | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Construction services | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	(336)	0
Construction services | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	750,844	706,345	2,059,733	2,184,632
Other revenues	10,142	11,061	29,978	34,040
Total external operating revenues	760,986	717,406	2,089,711	2,218,672
Construction services | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Construction services | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Construction services | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	534,613	514,378	1,476,006	1,672,948
Construction services | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	216,062	192,056	583,803	511,563
Construction services | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	169	(89)	260	121
Construction services | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Construction services | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Construction services | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Construction services | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(1,432)	(1,689)	(4,265)	(6,412)
Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1	0	18	0
Other revenues	0	0	0	0
Total external operating revenues	1	0	18	0
Other | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Electrical & mechanical specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Transmission & distribution specialty contracting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,433	1,689	4,283	6,412
Other | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 0	$ 0	$ 0	$ 0