Segment Information - Summary of segment's internal financial reports (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Contract revenues:	$ 610,182	$ 607,901	$ 1,852,241	$ 1,639,422
Income from operations:	30,952	24,929	88,028	60,679
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Income from operations:	(18,488)	(19,190)	(51,644)	(43,512)
T&D
Segment Reporting Information [Line Items]
Contract revenues:	306,546	299,739	948,285	835,768
T&D | Operating Segments
Segment Reporting Information [Line Items]
Income from operations:	35,301	32,387	96,737	74,189
C&I
Segment Reporting Information [Line Items]
Contract revenues:	303,636	308,162	903,956	803,654
C&I | Operating Segments
Segment Reporting Information [Line Items]
Income from operations:	$ 14,139	$ 11,732	$ 42,935	$ 30,002