Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Operating revenues:	$ 1,000,795	$ 1,002,487	$ 3,522,020	$ 3,119,351
Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	48,388	44,054	142,941	131,432
Natural gas storage
Disaggregation of Revenue [Line Items]
Operating revenues:	4,808	3,595	12,427	10,210
Electrical & mechanical specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	514,378	543,717	1,672,948	1,443,758
Transmission & distribution specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	192,056	181,550	511,563	496,190
Other
Disaggregation of Revenue [Line Items]
Operating revenues:	24,098	19,739	66,231	56,507
Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	991,276	989,085	3,493,191	3,090,046
Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	9,519	13,402	28,829	29,305
Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	103,036	101,055	620,304	543,287
Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	90,114	82,519	440,846	388,097
Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	18,019	18,047	65,173	61,309
Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	1,865	2,002	5,349	5,632
Electric
Disaggregation of Revenue [Line Items]
Operating revenues:	108,089	99,283	294,775	278,518
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(27)	(34)	(82)	(102)
Electric | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	14,701	10,758	38,111	33,727
Electric | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	111,343	99,330	302,574	283,372
Electric | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	(3,254)	(47)	(7,799)	(4,854)
Electric | Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	34,303	36,981	102,953	103,648
Electric | Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	49,754	38,785	124,363	108,400
Electric | Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	10,747	10,838	31,880	32,067
Electric | Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	1,865	2,002	5,349	5,632
Natural gas distribution
Disaggregation of Revenue [Line Items]
Operating revenues:	134,896	132,145	919,487	793,142
Natural gas distribution | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(69)	(69)	(208)	(206)
Natural gas distribution | Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	13,050	11,910	38,225	35,747
Natural gas distribution | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	3,881	3,495	11,874	9,854
Natural gas distribution | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	133,227	130,353	917,018	793,973
Natural gas distribution | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	1,669	1,792	2,469	(831)
Natural gas distribution | Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	68,733	64,074	517,351	439,639
Natural gas distribution | Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	40,360	43,734	316,483	279,697
Natural gas distribution | Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	7,272	7,209	33,293	29,242
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:	40,404	36,058	89,086	76,997
Pipeline | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(3,701)	(3,581)	(37,889)	(37,309)
Pipeline | Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	35,338	32,144	104,716	95,685
Pipeline | Natural gas storage
Disaggregation of Revenue [Line Items]
Operating revenues:	4,808	3,595	12,427	10,210
Pipeline | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	3,916	3,814	9,713	8,201
Pipeline | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	40,361	35,972	88,967	76,787
Pipeline | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	43	86	119	210
Construction services
Disaggregation of Revenue [Line Items]
Operating revenues:	717,406	735,001	2,218,672	1,970,694
Construction services | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	0	(2,037)	0	(4,391)
Construction services | Electrical & mechanical specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	514,378	543,717	1,672,948	1,443,758
Construction services | Transmission & distribution specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	192,056	181,550	511,563	496,190
Construction services | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	(89)	200	121	357
Construction services | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	706,345	723,430	2,184,632	1,935,914
Construction services | Revenues out of scope
Disaggregation of Revenue [Line Items]
Operating revenues:	11,061	11,571	34,040	34,780
Other
Disaggregation of Revenue [Line Items]
Operating revenues:	0	0	0	0
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(1,689)	(1,472)	(6,412)	(4,368)
Other | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	1,689	1,472	6,412	4,368
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
Consolidated Operations | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	$ (5,486)	$ (7,193)	$ (44,591)	$ (46,376)