Concentration of Credit Risk - Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 27, 2019	Jul. 28, 2018	Jul. 27, 2019	Jul. 28, 2018
Concentration Risk
Contract revenues	$ 884,221	$ 799,470	$ 1,717,964	$ 1,530,844
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	$ 804,400	$ 726,700	$ 1,565,800	$ 1,393,900
Concentration risk percentage	91.00%	90.90%	91.20%	91.10%
Customer Concentration Risk | Sales Revenue, Services, Net | Underground facility locating
Concentration Risk
Contract revenues	$ 53,800	$ 49,000	$ 102,000	$ 94,100
Concentration risk percentage	6.10%	6.10%	5.90%	6.10%
Customer Concentration Risk | Sales Revenue, Services, Net | Electrical and gas utilities and other
Concentration Risk
Contract revenues	$ 26,000	$ 23,800	$ 50,200	$ 42,800
Concentration risk percentage	2.90%	3.00%	2.90%	2.80%
Five Unnamed Customers | Customer Concentration Risk | Sales Revenue, Services, Net
Concentration Risk
Concentration risk percentage			79.40%	78.30%