Disaggregation of revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 6,973,864	$ 5,680,733	$ 5,532,750
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(84,176)	(77,606)	(76,969)
Internal sales
Disaggregation of Revenue [Line Items]
Revenues	(593,882)	(501,044)	(550,815)
Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues	178,176	162,409	157,232
Natural Gas Gathering [Member]
Disaggregation of Revenue [Line Items]
Revenues			4,865
Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues	14,583	14,680	14,918
Contracting services
Disaggregation of Revenue [Line Items]
Revenues	1,187,721	1,017,471	1,069,665
Construction materials
Disaggregation of Revenue [Line Items]
Revenues	1,940,890	1,712,503	1,659,152
Electrical & mechanical specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	1,988,729	1,324,419	1,397,124
Transmission & distribution specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	662,705	677,074	649,486
Other
Disaggregation of Revenue [Line Items]
Revenues	88,716	81,407	68,865
Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	6,933,344	5,628,488	5,471,545
Other revenues
Disaggregation of Revenue [Line Items]
Revenues	40,520	52,245	61,205
Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues	856,825	671,562	599,051
Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues	599,984	465,841	409,350
Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues	85,476	72,721	62,987
Other utility sales
Disaggregation of Revenue [Line Items]
Revenues	7,597	7,051	6,634
Electric
Disaggregation of Revenue [Line Items]
Revenues	376,579	349,039	331,538
Electric | Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(494)	(543)	(491)
Electric | Other
Disaggregation of Revenue [Line Items]
Revenues	45,608	42,902	32,452
Electric | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	381,293	355,564	329,479
Electric | Other revenues
Disaggregation of Revenue [Line Items]
Revenues	(4,714)	(6,525)	2,059
Electric | Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues	138,634	126,841	122,663
Electric | Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues	146,182	137,556	131,477
Electric | Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues	43,766	41,757	36,744
Electric | Other utility sales
Disaggregation of Revenue [Line Items]
Revenues	7,597	7,051	6,634
Natural gas distribution
Disaggregation of Revenue [Line Items]
Revenues	1,273,249	971,364	847,651
Natural gas distribution | Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(555)	(576)	(534)
Natural gas distribution | Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues	48,886	48,408	45,546
Natural gas distribution | Other
Disaggregation of Revenue [Line Items]
Revenues	13,617	10,567	10,753
Natural gas distribution | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	1,275,651	962,369	836,269
Natural gas distribution | Other revenues
Disaggregation of Revenue [Line Items]
Revenues	(2,402)	8,995	11,382
Natural gas distribution | Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues	718,191	544,721	476,388
Natural gas distribution | Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues	453,802	328,285	277,873
Natural gas distribution | Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues	41,710	30,964	26,243
Natural gas distribution | Other utility sales
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Pipeline
Disaggregation of Revenue [Line Items]
Revenues	96,567	82,858	85,346
Pipeline | Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(59,012)	(59,678)	(58,531)
Pipeline | Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues	129,290	114,001	111,686
Pipeline | Natural Gas Gathering [Member]
Disaggregation of Revenue [Line Items]
Revenues			4,865
Pipeline | Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues	14,583	14,680	14,918
Pipeline | Other
Disaggregation of Revenue [Line Items]
Revenues	11,450	13,667	12,216
Pipeline | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	96,311	82,670	85,154
Pipeline | Other revenues
Disaggregation of Revenue [Line Items]
Revenues	256	188	192
Construction materials and contracting
Disaggregation of Revenue [Line Items]
Revenues	2,533,713	2,228,306	2,177,585
Construction materials and contracting | Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(1,016)	(624)	(417)
Construction materials and contracting | Internal sales
Disaggregation of Revenue [Line Items]
Revenues	(593,882)	(501,044)	(550,815)
Construction materials and contracting | Contracting services
Disaggregation of Revenue [Line Items]
Revenues	1,187,721	1,017,471	1,069,665
Construction materials and contracting | Construction materials
Disaggregation of Revenue [Line Items]
Revenues	1,940,890	1,712,503	1,659,152
Construction materials and contracting | Other
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Construction materials and contracting | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	2,533,713	2,228,306	2,177,585
Construction materials and contracting | Other revenues
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Construction services
Disaggregation of Revenue [Line Items]
Revenues	2,693,756	2,049,082	2,090,685
Construction services | Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(5,494)	(2,555)	(5,038)
Construction services | Electrical & mechanical specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	1,988,729	1,324,419	1,397,124
Construction services | Transmission & distribution specialty contracting
Disaggregation of Revenue [Line Items]
Revenues	662,705	677,074	649,486
Construction services | Other
Disaggregation of Revenue [Line Items]
Revenues	436	557	1,541
Construction services | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	2,646,376	1,999,495	2,043,113
Construction services | Other revenues
Disaggregation of Revenue [Line Items]
Revenues	47,380	49,587	47,572
Other
Disaggregation of Revenue [Line Items]
Revenues	0	84	(55)
Other | Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(17,605)	(13,630)	(11,958)
Other | Other
Disaggregation of Revenue [Line Items]
Revenues	17,605	13,714	11,903
Other | Revenues from contracts with customers
Disaggregation of Revenue [Line Items]
Revenues	0	84	(55)
Other | Other revenues
Disaggregation of Revenue [Line Items]
Revenues	$ 0	$ 0	$ 0