Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Operating revenues:	$ 1,091,126	$ 1,009,749	$ 2,521,224	$ 2,116,864
Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(11,165)	(10,875)	(39,105)	(39,183)
Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	46,065	43,423	94,553	87,378
Natural gas storage
Disaggregation of Revenue [Line Items]
Operating revenues:	3,758	2,896	7,620	6,615
Electrical & mechanical specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	568,307	507,233	1,158,570	900,041
Transmission & distribution specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	167,485	166,174	319,507	314,640
Other
Disaggregation of Revenue [Line Items]
Operating revenues:	22,068	18,208	42,132	36,768
Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	1,079,031	1,001,352	2,501,913	2,100,961
Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	12,095	8,397	19,311	15,903
Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	151,792	146,112	517,267	442,232
Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	109,458	106,369	350,731	305,578
Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	19,553	19,932	47,154	43,262
Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	1,710	1,880	3,484	3,630
Electric
Disaggregation of Revenue [Line Items]
Operating revenues:	90,989	85,551	186,686	179,235
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(27)	(34)	(55)	(68)
Electric | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	11,531	10,216	23,410	22,969
Electric | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	92,671	86,363	191,231	184,042
Electric | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	(1,682)	(812)	(4,545)	(4,807)
Electric | Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	30,825	29,363	68,650	66,667
Electric | Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	38,262	34,015	74,609	69,615
Electric | Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	10,370	10,923	21,133	21,229
Electric | Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	1,710	1,880	3,484	3,630
Natural gas distribution
Disaggregation of Revenue [Line Items]
Operating revenues:	218,995	210,510	784,590	660,998
Natural gas distribution | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(69)	(71)	(139)	(137)
Natural gas distribution | Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	11,671	11,456	25,175	23,837
Natural gas distribution | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	3,272	3,751	7,993	6,360
Natural gas distribution | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	216,220	213,248	783,789	663,621
Natural gas distribution | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	2,775	(2,738)	801	(2,623)
Natural gas distribution | Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	120,967	116,749	448,617	375,565
Natural gas distribution | Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	71,196	72,354	276,122	235,963
Natural gas distribution | Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	9,183	9,009	26,021	22,033
Natural gas distribution | Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	0	0	0	0
Pipeline
Disaggregation of Revenue [Line Items]
Operating revenues:	34,209	29,818	48,683	40,938
Pipeline | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(7,918)	(7,787)	(34,188)	(33,729)
Pipeline | Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	34,394	31,967	69,378	63,541
Pipeline | Natural gas storage
Disaggregation of Revenue [Line Items]
Operating revenues:	3,758	2,896	7,620	6,615
Pipeline | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	3,937	2,676	5,797	4,387
Pipeline | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	34,171	29,752	48,607	40,814
Pipeline | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	38	66	76	124
Construction services
Disaggregation of Revenue [Line Items]
Operating revenues:	746,933	683,870	1,501,265	1,235,693
Construction services | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	0	(1,527)	0	(2,353)
Construction services | Electrical & mechanical specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	568,307	507,233	1,158,570	900,041
Construction services | Transmission & distribution specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	167,485	166,174	319,507	314,640
Construction services | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	177	109	209	156
Construction services | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	735,969	671,989	1,478,286	1,212,484
Construction services | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	10,964	11,881	22,979	23,209
Other
Disaggregation of Revenue [Line Items]
Operating revenues:	0	0	0	0
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(3,151)	(1,456)	(4,723)	(2,896)
Other | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	3,151	1,456	4,723	2,896
Other | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	0	0	0	0
Other | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	$ 0	$ 0	$ 0	$ 0