Concentration of Credit Risk - Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 28, 2018	Jul. 29, 2017	Jul. 28, 2018	Jul. 29, 2017
Concentration Risk
Contract revenues	$ 799,470	$ 780,188	$ 1,530,844	$ 1,566,526
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	$ 726,700	$ 712,000	$ 1,393,900	$ 1,437,400
Concentration risk percentage	90.90%	91.30%	91.10%	91.80%
Customer Concentration Risk | Sales Revenue, Services, Net | Underground facility locating
Concentration Risk
Contract revenues	$ 49,000	$ 47,500	$ 94,100	$ 89,600
Concentration risk percentage	6.10%	6.10%	6.10%	5.70%
Customer Concentration Risk | Sales Revenue, Services, Net | Electrical and gas utilities and other
Concentration Risk
Contract revenues	$ 23,800	$ 20,700	$ 42,800	$ 39,500
Concentration risk percentage	3.00%	2.60%	2.80%	2.50%
Five Unnamed Customers | Customer Concentration Risk | Sales Revenue, Services, Net
Concentration Risk
Concentration risk percentage			78.30%	77.60%