Business segment data - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Revenues	$ 1,213,825	$ 1,430,098
Operating income	135,947	118,521
Income from continuing operations	100,898	83,875
Discontinued operations, net of tax	0	(45,522)
Net income	100,898	38,353
Operating Segments
Segment Reporting Information [Line Items]
Revenues	1,244,291	1,456,465
Operating Segments | Electric
Segment Reporting Information [Line Items]
Revenues	107,727	95,697
Operating income	22,788	21,091
Operating Segments | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	459,469	565,597
Operating income	58,238	58,505
Operating Segments | Pipeline
Segment Reporting Information [Line Items]
Revenues	21,011	14,471
Operating income	22,650	13,040
Operating Segments | Construction services
Segment Reporting Information [Line Items]
Revenues	625,602	754,333
Operating income	38,884	35,217
Operating Segments | Other
Segment Reporting Information [Line Items]
Revenues	16	0
Operating income	(6,613)	(9,332)
Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(31,899)	(27,939)
Regulated operation
Segment Reporting Information [Line Items]
Revenues	586,017	673,932
Income from continuing operations	73,343	64,464
Regulated operation | Operating Segments
Segment Reporting Information [Line Items]
Revenues	586,017	673,932
Regulated operation | Operating Segments | Electric
Segment Reporting Information [Line Items]
Revenues	107,727	95,697
Income from continuing operations	17,869	16,607
Regulated operation | Operating Segments | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	459,469	565,597
Income from continuing operations	40,070	38,928
Regulated operation | Operating Segments | Pipeline
Segment Reporting Information [Line Items]
Revenues	18,821	12,638
Income from continuing operations	15,404	8,929
Regulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(30,359)	(26,356)
Regulated operation | Intersegment eliminations | Electric
Segment Reporting Information [Line Items]
Revenues	(28)	(27)
Regulated operation | Intersegment eliminations | Natural gas distribution
Segment Reporting Information [Line Items]
Revenues	(56)	(70)
Regulated operation | Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	(30,275)	(26,259)
Nonregulated operation
Segment Reporting Information [Line Items]
Revenues	627,808	756,166
Income from continuing operations	27,555	19,411
Nonregulated operation | Operating Segments
Segment Reporting Information [Line Items]
Revenues	627,808	756,166
Nonregulated operation | Operating Segments | Pipeline
Segment Reporting Information [Line Items]
Revenues	2,190	1,833
Income from continuing operations	(346)	(458)
Nonregulated operation | Operating Segments | Construction services
Segment Reporting Information [Line Items]
Revenues	625,602	754,333
Income from continuing operations	28,214	28,809
Nonregulated operation | Operating Segments | Other
Segment Reporting Information [Line Items]
Revenues	16	0
Income from continuing operations	(313)	(8,940)
Nonregulated operation | Intersegment eliminations
Segment Reporting Information [Line Items]
Revenues	(1,540)	(1,583)
Nonregulated operation | Intersegment eliminations | Pipeline
Segment Reporting Information [Line Items]
Revenues	(36)	(11)
Nonregulated operation | Intersegment eliminations | Construction services
Segment Reporting Information [Line Items]
Revenues	(87)	0
Nonregulated operation | Intersegment eliminations | Other
Segment Reporting Information [Line Items]
Revenues	$ (1,417)	$ (1,572)