Reportable Segments (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)
Segment reporting information
Number of reportable segments | segment			5
Revenue	$ 908,216	$ 789,929	$ 1,651,459	$ 1,451,487
% of Total Revenue	100.00%	100.00%	100.00%	100.00%
Gross Profit	$ 100,967	$ 80,531	$ 148,777	$ 132,991
% of Revenue	11.10%	10.20%	9.00%	9.20%
Power
Segment reporting information
Revenue	$ 157,476	$ 172,170	$ 353,669	$ 317,553
% of Total Revenue	17.30%	21.80%	21.40%	21.90%
Gross Profit	$ 6,703	$ 23,167	$ 25,385	$ 43,365
% of Revenue	4.30%	13.50%	7.20%	13.70%
Pipeline
Segment reporting information
Revenue	$ 289,559	$ 137,243	$ 481,082	$ 272,057
% of Total Revenue	31.90%	17.40%	29.10%	18.70%
Gross Profit	$ 27,030	$ 11,531	$ 43,522	$ 26,547
% of Revenue	9.30%	8.40%	9.00%	9.80%
Utilities
Segment reporting information
Revenue	$ 230,175	$ 222,312	$ 377,345	$ 368,518
% of Total Revenue	25.40%	28.10%	22.90%	25.40%
Gross Profit	$ 42,392	$ 30,866	$ 46,994	$ 39,107
% of Revenue	18.40%	13.90%	12.50%	10.60%
Transmission
Segment reporting information
Revenue	$ 109,948	$ 135,354	$ 212,732	$ 253,797
% of Total Revenue	12.10%	17.10%	12.90%	17.50%
Gross Profit	$ 13,445	$ 10,200	$ 15,157	$ 16,828
% of Revenue	12.20%	7.50%	7.10%	6.60%
Civil
Segment reporting information
Revenue	$ 121,058	$ 122,850	$ 226,631	$ 239,562
% of Total Revenue	13.30%	15.60%	13.70%	16.50%
Gross Profit	$ 11,397	$ 4,767	$ 17,719	$ 7,144
% of Revenue	9.40%	3.90%	7.80%	3.00%