Reportable Segments (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)
Segment reporting information
Number of reportable segments | segment	5
Revenue	$ 743,243	$ 661,558
% of Total Revenue	100.00%	100.00%
Gross Profit	$ 47,810	$ 52,460
% of Revenue	6.40%	7.90%
Power
Segment reporting information
Revenue	$ 196,193	$ 145,383
% of Total Revenue	26.40%	22.00%
Gross Profit	$ 18,682	$ 20,198
% of Revenue	9.50%	13.90%
Pipeline
Segment reporting information
Revenue	$ 191,523	$ 134,814
% of Total Revenue	25.80%	20.40%
Gross Profit	$ 16,492	$ 15,016
% of Revenue	8.60%	11.10%
Utilities
Segment reporting information
Revenue	$ 147,170	$ 146,206
% of Total Revenue	19.80%	22.10%
Gross Profit	$ 4,602	$ 8,241
% of Revenue	3.10%	5.60%
Transmission
Segment reporting information
Revenue	$ 102,784	$ 118,443
% of Total Revenue	13.80%	17.90%
Gross Profit	$ 1,712	$ 6,628
% of Revenue	1.70%	5.60%
Civil
Segment reporting information
Revenue	$ 105,573	$ 116,712
% of Total Revenue	14.20%	17.60%
Gross Profit	$ 6,322	$ 2,377
% of Revenue	6.00%	2.00%