Customer Concentration and Revenue Information - Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 25, 2020	Jul. 27, 2019	Jul. 25, 2020	Jul. 27, 2019
Concentration Risk
Contract revenues	$ 823,921	$ 884,221	$ 1,638,244	$ 1,717,964
% of Total	100.00%	100.00%	100.00%	100.00%
Customer Concentration Risk | Revenue Benchmark
Concentration Risk
% of Total			10.00%
Customer Concentration Risk | Revenue Benchmark | Telecommunications
Concentration Risk
Contract revenues	$ 746,700	$ 804,400	$ 1,472,700	$ 1,565,800
% of Total	90.60%	91.00%	89.90%	91.10%
Customer Concentration Risk | Revenue Benchmark | Underground facility locating
Concentration Risk
Contract revenues	$ 58,900	$ 53,800	$ 112,300	$ 102,000
% of Total	7.20%	6.10%	6.90%	5.90%
Customer Concentration Risk | Revenue Benchmark | Electrical and gas utilities and other
Concentration Risk
Contract revenues	$ 18,300	$ 26,000	$ 53,200	$ 50,200
% of Total	2.20%	2.90%	3.20%	3.00%
Five Unnamed Customers | Customer Concentration Risk | Revenue Benchmark
Concentration Risk
% of Total			77.50%	79.40%