Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Operating revenues:	$ 1,977,206	$ 1,586,013	$ 5,114,686	$ 4,237,608
Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(10,868)	(7,983)	(57,047)	(51,356)
Intrasegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(259,761)	(201,630)	(475,026)	(394,126)
Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	44,054	39,870	131,432	120,875
Natural gas storage
Disaggregation of Revenue [Line Items]
Operating revenues:	3,595	3,483	10,210	10,606
Contracting services
Disaggregation of Revenue [Line Items]
Operating revenues:	492,207	415,106	937,156	791,964
Construction materials
Disaggregation of Revenue [Line Items]
Operating revenues:	742,982	617,823	1,535,077	1,332,997
Electrical & mechanical specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	543,717	317,238	1,443,758	1,020,130
Transmission & distribution specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	181,550	185,842	496,190	502,328
Other
Disaggregation of Revenue [Line Items]
Operating revenues:	22,705	21,487	65,306	60,820
Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	1,963,804	1,575,186	5,085,381	4,200,691
Other revenues
Disaggregation of Revenue [Line Items]
Operating revenues:	13,402	10,827	29,305	36,917
Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	101,055	91,696	543,287	441,007
Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	82,519	74,371	388,097	308,797
Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	18,047	15,890	61,309	51,265
Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	2,002	1,993	5,632	5,384
Electric
Disaggregation of Revenue [Line Items]
Operating revenues:	99,193	98,930	278,249	267,254
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(124)	(136)	(371)	(407)
Electric | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	10,758	12,589	33,727	31,827
Electric | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	99,240	100,386	283,103	272,583
Electric | Other revenues
Disaggregation of Revenue [Line Items]
Operating revenues:	(47)	(1,456)	(4,854)	(5,329)
Electric | Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	36,981	36,412	103,648	99,106
Electric | Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	38,785	39,033	108,400	105,795
Electric | Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	10,838	10,495	32,067	30,878
Electric | Other utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	2,002	1,993	5,632	5,384
Natural gas distribution
Disaggregation of Revenue [Line Items]
Operating revenues:	132,074	110,378	792,932	614,373
Natural gas distribution | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(139)	(142)	(416)	(425)
Natural gas distribution | Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	11,910	11,812	35,747	35,715
Natural gas distribution | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	3,494	2,110	9,854	7,913
Natural gas distribution | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	130,282	109,797	793,763	608,493
Natural gas distribution | Other revenues
Disaggregation of Revenue [Line Items]
Operating revenues:	1,792	581	(831)	5,880
Natural gas distribution | Residential utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	64,074	55,284	439,639	341,901
Natural gas distribution | Commercial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	43,734	35,338	279,697	203,002
Natural gas distribution | Industrial utility sales
Disaggregation of Revenue [Line Items]
Operating revenues:	7,209	5,395	29,242	20,387
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:	36,045	30,968	76,977	68,653
Pipeline | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(3,595)	(3,908)	(37,328)	(38,000)
Pipeline | Natural gas transportation
Disaggregation of Revenue [Line Items]
Operating revenues:	32,144	28,058	95,685	85,160
Pipeline | Natural gas storage
Disaggregation of Revenue [Line Items]
Operating revenues:	3,595	3,483	10,210	10,606
Pipeline | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	3,815	3,290	8,200	10,760
Pipeline | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	35,959	30,923	76,767	68,526
Pipeline | Other revenues
Disaggregation of Revenue [Line Items]
Operating revenues:	86	45	210	127
Construction materials and contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	975,085	831,189	1,996,533	1,730,521
Construction materials and contracting | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(343)	(110)	(674)	(314)
Construction materials and contracting | Intrasegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(259,761)	(201,630)	(475,026)	(394,126)
Construction materials and contracting | Contracting services
Disaggregation of Revenue [Line Items]
Operating revenues:	492,207	415,106	937,156	791,964
Construction materials and contracting | Construction materials
Disaggregation of Revenue [Line Items]
Operating revenues:	742,982	617,823	1,535,077	1,332,997
Construction materials and contracting | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	0	0	0	0
Construction materials and contracting | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	975,085	831,189	1,996,533	1,730,521
Construction materials and contracting | Other revenues
Disaggregation of Revenue [Line Items]
Operating revenues:	0	0	0	0
Construction services
Disaggregation of Revenue [Line Items]
Operating revenues:	734,809	514,523	1,969,995	1,556,737
Construction services | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(2,229)	(289)	(5,090)	(2,128)
Construction services | Electrical & mechanical specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	543,717	317,238	1,443,758	1,020,130
Construction services | Transmission & distribution specialty contracting
Disaggregation of Revenue [Line Items]
Operating revenues:	181,550	185,842	496,190	502,328
Construction services | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	200	75	357	168
Construction services | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	723,238	502,866	1,935,215	1,520,498
Construction services | Other revenues
Disaggregation of Revenue [Line Items]
Operating revenues:	11,571	11,657	34,780	36,239
Other
Disaggregation of Revenue [Line Items]
Operating revenues:	0	25	0	70
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Operating revenues:	(4,438)	(3,398)	(13,168)	(10,082)
Other | Other
Disaggregation of Revenue [Line Items]
Operating revenues:	4,438	3,423	13,168	10,152
Other | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Operating revenues:	0	25	0	70
Other | Other revenues
Disaggregation of Revenue [Line Items]
Operating revenues:	$ 0	$ 0	$ 0	$ 0