Concentration of Credit Risk - Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 25, 2020	Apr. 27, 2019
Concentration Risk
Contract revenues	$ 814,322	$ 833,743
Concentration risk percentage	100.00%	100.00%
Customer Concentration Risk | Revenue Benchmark
Concentration Risk
Concentration risk percentage	10.00%
Customer Concentration Risk | Revenue Benchmark | Telecommunications
Concentration Risk
Contract revenues	$ 726,000	$ 761,400
Concentration risk percentage	89.20%	91.30%
Customer Concentration Risk | Revenue Benchmark | Underground facility locating
Concentration Risk
Contract revenues	$ 53,300	$ 48,200
Concentration risk percentage	6.50%	5.80%
Customer Concentration Risk | Revenue Benchmark | Electrical and gas utilities and other
Concentration Risk
Contract revenues	$ 35,000	$ 24,100
Concentration risk percentage	4.30%	2.90%
Five Unnamed Customers | Customer Concentration Risk | Revenue Benchmark
Concentration Risk
Concentration risk percentage	78.50%	80.40%