Concentration of Credit Risk - Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 26, 2019	Oct. 27, 2018	Oct. 26, 2019	Oct. 27, 2018
Concentration Risk
Contract revenues	$ 884,115	$ 848,237	$ 2,602,079	$ 2,379,081
Concentration risk percentage	100.00%	100.00%	100.00%	100.00%
Customer Concentration Risk | Sales Revenue, Services, Net
Concentration Risk
Concentration risk percentage			10.00%
Customer Concentration Risk | Sales Revenue, Services, Net | Telecommunications
Concentration Risk
Contract revenues	$ 798,100	$ 773,200	$ 2,363,900	$ 2,167,100
Concentration risk percentage	90.30%	91.10%	90.80%	91.10%
Customer Concentration Risk | Sales Revenue, Services, Net | Underground facility locating
Concentration Risk
Contract revenues	$ 56,000	$ 48,800	$ 158,000	$ 142,900
Concentration risk percentage	6.30%	5.80%	6.10%	6.00%
Customer Concentration Risk | Sales Revenue, Services, Net | Electrical and gas utilities and other
Concentration Risk
Contract revenues	$ 30,000	$ 26,200	$ 80,200	$ 69,100
Concentration risk percentage	3.40%	3.10%	3.10%	2.90%
Five Unnamed Customers | Customer Concentration Risk | Sales Revenue, Services, Net
Concentration Risk
Concentration risk percentage			78.70%	78.30%