Segment Information - Summary of segment's internal financial reports (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Contract revenues:	$ 592,486	$ 518,470
Income from operations:	27,411	16,408
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Income from operations:	(15,534)	(10,868)
T&D
Segment Reporting Information [Line Items]
Contract revenues:	314,908	259,270
T&D | Operating Segments
Segment Reporting Information [Line Items]
Income from operations:	28,673	17,964
C&I
Segment Reporting Information [Line Items]
Contract revenues:	277,578	259,200
C&I | Operating Segments
Segment Reporting Information [Line Items]
Income from operations:	$ 14,272	$ 9,312