Business Segment Data - Summary of Segment Reporting Information by Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Operating revenue	$ (760,985)	$ (717,406)	$ (2,090,047)	$ (2,218,672)
Operating income	53,709	50,091	143,902	139,619
Interest expense (benefit)	2,851	4,596	8,823	13,483
Income tax expense	13,995	11,423	37,606	32,822
Operating segments
Segment Reporting Information [Line Items]
Operating revenue	(765,399)	(721,361)	(2,105,555)	(2,229,661)
Operating income	60,201	54,091	160,853	151,582
Eliminations
Segment Reporting Information [Line Items]
Operating revenue	4,414	3,955	15,508	10,989
Electrical & Mechanical
Segment Reporting Information [Line Items]
Operating revenue	(534,741)	(514,378)	(1,476,151)	(1,672,948)
Electrical & Mechanical | Operating segments
Segment Reporting Information [Line Items]
Operating revenue	(536,895)	(516,933)	(1,481,778)	(1,680,210)
Depreciation and amortization expense	1,618	1,557	4,794	4,643
Operating income	34,943	31,076	100,771	100,268
Interest expense (benefit)	(54)	1,391	117	4,645
Income tax expense	9,806	7,509	28,478	25,214
Capital expenditures	2,701	823	5,641	3,714
Electrical & Mechanical | Eliminations
Segment Reporting Information [Line Items]
Operating revenue	2,154	2,555	5,627	7,262
Transmission & Distribution
Segment Reporting Information [Line Items]
Operating revenue	(226,244)	(203,028)	(613,896)	(545,724)
Transmission & Distribution | Operating segments
Segment Reporting Information [Line Items]
Operating revenue	(228,504)	(204,428)	(623,777)	(549,451)
Depreciation and amortization expense	4,753	4,412	13,848	12,697
Operating income	25,258	23,015	60,082	51,314
Interest expense (benefit)	982	1,367	3,030	3,239
Income tax expense	6,249	5,587	14,596	11,996
Capital expenditures	15,256	6,583	28,726	23,983
Transmission & Distribution | Eliminations
Segment Reporting Information [Line Items]
Operating revenue	$ 2,260	$ 1,400	$ 9,881	$ 3,727