Business segment data - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Revenues	$ 1,050,516			$ 1,000,795			$ 3,311,886	$ 3,522,020
Operating income	90,804			84,604			316,497	285,157
Income from continuing operations	62,159			78,218			223,631	309,726
Discontinued operations, net of tax	2,456			(3,289)			2,319	(65,752)
Net income	64,615	$ 60,436	$ 100,898	74,929	$ 130,692	$ 38,353	225,950	243,974
Operating Segments
Segment Reporting Information [Line Items]
Revenues	1,054,646			1,004,592			3,355,897	3,560,199
Operating Segments | Electric
Segment Reporting Information [Line Items]
Revenues	108,384			108,089			315,268	294,775
Operating income	32,079			28,718			73,498	71,372
Operating Segments | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	133,517			134,896			794,418	919,487
Operating income	(14,695)			(15,258)			44,747	45,674
Operating Segments | Pipeline
Segment Reporting Information [Line Items]
Revenues	47,628			40,404			112,471	89,086
Operating income	22,179			17,767			68,101	44,693
Operating Segments | Construction services
Segment Reporting Information [Line Items]
Revenues	760,986			717,406			2,089,711	2,218,672
Operating income	53,709			50,091			143,902	139,619
Operating Segments | Other
Segment Reporting Information [Line Items]
Revenues	1			0			18	0
Operating income	(2,468)			3,286			(13,751)	(16,201)
Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(5,563)			(5,486)			(48,294)	(44,591)
Regulated operation
Segment Reporting Information [Line Items]
Revenues	286,053			279,534			1,212,615	1,293,959
Income from continuing operations	21,621			14,628			122,324	100,923
Regulated operation | Operating Segments
Segment Reporting Information [Line Items]
Revenues	286,053			279,534			1,212,615	1,293,959
Regulated operation | Operating Segments | Electric
Segment Reporting Information [Line Items]
Revenues	108,384			108,089			315,268	294,775
Income from continuing operations	24,292			20,942			57,689	53,887
Regulated operation | Operating Segments | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	133,517			134,896			794,418	919,487
Income from continuing operations	(17,481)			(17,764)			17,581	18,007
Regulated operation | Operating Segments | Pipeline
Segment Reporting Information [Line Items]
Revenues	44,152			36,549			102,929	79,697
Income from continuing operations	14,810			11,450			47,054	29,029
Regulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(4,104)			(3,762)			(43,430)	(37,914)
Regulated operation | Intersegment eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	(96)			(27)			(188)	(82)
Regulated operation | Intersegment eliminations | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	(104)			(69)			(209)	(208)
Regulated operation | Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	(3,904)			(3,666)			(43,033)	(37,624)
Nonregulated operation
Segment Reporting Information [Line Items]
Revenues	764,463			721,261			2,099,271	2,228,061
Income from continuing operations	40,538			63,590			101,307	208,803
Nonregulated operation | Operating Segments
Segment Reporting Information [Line Items]
Revenues	764,463			721,261			2,099,271	2,228,061
Nonregulated operation | Operating Segments | Pipeline
Segment Reporting Information [Line Items]
Revenues	3,476			3,855			9,542	9,389
Income from continuing operations	374			508			447	337
Nonregulated operation | Operating Segments | Construction services
Segment Reporting Information [Line Items]
Revenues	760,986			717,406			2,089,711	2,218,672
Income from continuing operations	41,767			35,975			108,953	105,951
Nonregulated operation | Operating Segments | Other
Segment Reporting Information [Line Items]
Revenues	1			0			18	0
Income from continuing operations	(1,603)			27,107			(8,093)	102,515
Nonregulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(1,459)			(1,724)			(4,864)	(6,677)
Nonregulated operation | Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	(27)			(35)			(263)	(265)
Nonregulated operation | Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	0			0			(336)	0
Nonregulated operation | Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	$ (1,432)			$ (1,689)			$ (4,265)	$ (6,412)