Revenue Recognition - Schedule of revenue by market type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disaggregation of Revenue [Line Items]
Amount	$ 583,214	$ 399,537	$ 1,500,084	$ 1,084,824
Revenue from Contract with Customer [Member]
Disaggregation of Revenue [Line Items]
Amount	$ 583,214	$ 399,537	$ 1,500,084	$ 1,084,824
Percent	100.00%	100.00%	100.00%	100.00%
T&D [Member] | Revenue from Contract with Customer [Member]
Disaggregation of Revenue [Line Items]
Amount	$ 294,940	$ 222,531	$ 823,398	$ 635,842
Percent	100.00%	100.00%	100.00%	100.00%
T&D [Member] | Market Type Transmission [Member] | Revenue from Contract with Customer [Member]
Disaggregation of Revenue [Line Items]
Amount	$ 196,083	$ 121,619	$ 553,314	$ 377,780
Percent	33.60%	30.40%	36.90%	34.80%
T&D [Member] | Market Type Distribution [Member] | Revenue from Contract with Customer [Member]
Disaggregation of Revenue [Line Items]
Amount	$ 98,857	$ 100,912	$ 270,084	$ 258,062
Percent	17.00%	25.30%	18.00%	23.80%
C&I [Member] | Revenue from Contract with Customer [Member]
Disaggregation of Revenue [Line Items]
Amount	$ 288,274	$ 177,006	$ 676,686	$ 448,982
Percent	100.00%	100.00%	100.00%	100.00%
C&I [Member] | Market Type Electrical construction [Member] | Revenue from Contract with Customer [Member]
Disaggregation of Revenue [Line Items]
Amount	$ 288,274	$ 177,006	$ 676,686	$ 448,982
Percent	49.40%	44.30%	45.10%	41.40%