Concentration of Credit Risk - Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended
	Apr. 27, 2019	Apr. 28, 2018
Concentration Risk
Contract revenues	$ 833,743	$ 731,375
Concentration risk percentage	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	$ 761,400	$ 667,200
Concentration risk percentage	91.30%	91.20%
Customer Concentration Risk | Sales Revenue, Services, Net | Underground facility locating
Concentration Risk
Contract revenues	$ 48,200	$ 45,100
Concentration risk percentage	5.80%	6.20%
Customer Concentration Risk | Sales Revenue, Services, Net | Electrical and gas utilities and other
Concentration Risk
Contract revenues	$ 24,100	$ 19,100
Concentration risk percentage	2.90%	2.60%
Five Unnamed Customers | Customer Concentration Risk | Sales Revenue, Services, Net
Concentration Risk
Concentration risk percentage	80.40%	78.80%