Revenue Recognition - Schedule of revenue by market type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Contract revenues	$ 610,182	$ 607,901	$ 1,852,241	$ 1,639,422
Product concentration risk | Revenue benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, Percent	100.00%	100.00%	100.00%	100.00%
T&D
Disaggregation of Revenue [Line Items]
Contract revenues	$ 306,546	$ 299,739	$ 948,285	$ 835,768
T&D | Product concentration risk | Revenue benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, Percent	100.00%	100.00%	100.00%	100.00%
T&D | Transmission
Disaggregation of Revenue [Line Items]
Contract revenues	$ 165,953	$ 185,007	$ 588,126	$ 537,762
T&D | Transmission | Product concentration risk | Revenue benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, Percent	27.20%	30.40%	31.80%	32.80%
T&D | Distribution
Disaggregation of Revenue [Line Items]
Contract revenues	$ 140,593	$ 114,732	$ 360,159	$ 298,006
T&D | Distribution | Product concentration risk | Revenue benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, Percent	23.00%	18.90%	19.40%	18.20%
C&I
Disaggregation of Revenue [Line Items]
Contract revenues	$ 303,636	$ 308,162	$ 903,956	$ 803,654
C&I | Product concentration risk | Revenue benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, Percent	100.00%	100.00%	100.00%	100.00%
C&I | Electrical construction
Disaggregation of Revenue [Line Items]
Contract revenues	$ 303,636	$ 308,162	$ 903,956	$ 803,654
C&I | Electrical construction | Product concentration risk | Revenue benchmark
Disaggregation of Revenue [Line Items]
Concentration risk, Percent	49.80%	50.70%	48.80%	49.00%