Customer Concentration and Revenue Information - Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2021	Jul. 25, 2020	Jul. 31, 2021	Jul. 25, 2020
Concentration Risk
Contract revenues	$ 787,568	$ 823,921	$ 1,515,065	$ 1,638,244
% of Total	100.00%	100.00%	100.00%	100.00%
Customer Concentration Risk | Revenue Benchmark | Telecommunications
Concentration Risk
Contract revenues	$ 697,500	$ 746,700	$ 1,337,200	$ 1,472,700
% of Total	88.60%	90.60%	88.30%	89.90%
Customer Concentration Risk | Revenue Benchmark | Underground facility locating
Concentration Risk
Contract revenues	$ 65,800	$ 58,900	$ 130,700	$ 112,300
% of Total	8.30%	7.20%	8.60%	6.90%
Customer Concentration Risk | Revenue Benchmark | Electrical and gas utilities and other
Concentration Risk
Contract revenues	$ 24,300	$ 18,300	$ 47,200	$ 53,200
% of Total	3.10%	2.20%	3.10%	3.20%
Five Unnamed Customers | Customer Concentration Risk | Revenue Benchmark
Concentration Risk
% of Total			66.50%	77.50%