Revenue Recognition - Schedule of revenue by market type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Amount	$ 448,776	$ 339,676	$ 916,870	$ 685,287
Sales Revenue, Net [Member]
Amount	$ 448,776	$ 339,676	$ 916,870	$ 685,287
Percent	100.00%	100.00%	100.00%	100.00%
T&D [Member] | Sales Revenue, Net [Member]
Amount	$ 255,910	$ 196,925	$ 528,458	$ 413,311
Percent	100.00%	100.00%	100.00%	100.00%
T&D [Member] | Market Type Transmission [Member] | Sales Revenue, Net [Member]
Amount	$ 169,466	$ 121,708	$ 357,231	$ 256,161
Percent	37.80%	35.80%	39.00%	37.40%
T&D [Member] | Market Type Distribution [Member] | Sales Revenue, Net [Member]
Amount	$ 86,444	$ 75,217	$ 171,227	$ 157,150
Percent	19.20%	22.20%	18.60%	22.90%
C&I [Member] | Sales Revenue, Net [Member]
Amount	$ 192,866	$ 142,751	$ 388,412	$ 271,976
Percent	100.00%	100.00%	100.00%	100.00%
C&I [Member] | Market Type Electrical construction [Member] | Sales Revenue, Net [Member]
Amount	$ 192,866	$ 142,751	$ 388,412	$ 271,976
Percent	43.00%	42.00%	42.40%	39.70%