Revenue from contracts with customers - Schedule of Disaggregation of revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 348,678	$ 343,120	$ 1,026,697	$ 931,324
Other revenues	2,508	1,351	(678)	1,422
Total external operating revenues	351,186	344,471	1,026,019	932,746
Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(10,208)	(9,138)	(43,995)	(39,503)
Total external operating revenues	(10,208)	(9,138)	(43,995)	(39,503)
Operating Segments
Disaggregation of Revenue [Line Items]
Total external operating revenues	361,215	353,587	1,069,656	972,190
Natural gas transportation
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	61,934	56,730	128,897	114,958
Natural gas storage
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,172	5,331	11,202	10,713
Other
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	33,905	23,085	76,514	44,210
Residential utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	128,610	138,127	457,530	440,452
Commercial utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	109,127	105,894	349,935	309,539
Industrial utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	18,345	21,026	42,971	46,954
Other utility sales
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,793	2,065	3,643	4,001
Electric | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(140)	(48)	(318)	(60)
Total external operating revenues	(140)	(48)	(318)	(60)
Electric | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	100,020	100,018	216,609	209,658
Other revenues	(2,134)	(845)	(6,462)	(2,742)
Total external operating revenues	97,886	99,173	210,147	206,916
Electric | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Electric | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Electric | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	17,123	13,186	34,714	28,816
Electric | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	28,569	31,437	68,254	70,659
Electric | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	43,428	41,620	91,905	83,135
Electric | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,247	11,758	18,411	23,107
Electric | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	1,793	2,065	3,643	4,001
Natural gas distribution | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(92)	(35)	(187)	(76)
Total external operating revenues	(92)	(35)	(187)	(76)
Natural gas distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	202,186	199,288	740,306	656,852
Other revenues	4,608	2,157	5,735	4,078
Total external operating revenues	206,794	201,445	746,041	660,930
Natural gas distribution | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	15,814	13,324	33,524	27,915
Natural gas distribution | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Natural gas distribution | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	11,626	5,767	35,103	8,969
Natural gas distribution | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	100,041	106,690	389,276	369,793
Natural gas distribution | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	65,699	64,274	258,030	226,404
Natural gas distribution | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	9,098	9,268	24,560	23,847
Natural gas distribution | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(9,796)	(9,035)	(43,132)	(39,325)
Total external operating revenues	(9,796)	(9,035)	(43,132)	(39,325)
Pipeline | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	46,473	43,812	69,782	64,797
Other revenues	34	39	49	86
Total external operating revenues	46,507	43,851	69,831	64,883
Pipeline | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	46,120	43,406	95,373	87,043
Pipeline | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	5,172	5,331	11,202	10,713
Pipeline | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	4,977	4,110	6,339	6,366
Pipeline | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Pipeline | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0	0	0
Other | Intersegment eliminations
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(180)	(20)	(358)	(42)
Total external operating revenues	(180)	(20)	(358)	(42)
Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	(1)	2	0	17
Other revenues	0	0		0
Total external operating revenues	(1)	2	0	17
Other | Natural gas transportation | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0		0
Other | Natural gas storage | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0		0
Other | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	179	22	358	59
Other | Residential utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0		0
Other | Commercial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0		0
Other | Industrial utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	0	0		0
Other | Other utility sales | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from contracts with customers	$ 0	$ 0		$ 0