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Concentration of Credit Risk - Customer Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Oct. 27, 2018	Oct. 28, 2017	Oct. 27, 2018	Oct. 28, 2017
Concentration Risk
Contract revenues	$ 848,237	$ 756,215	$ 2,379,081	$ 2,322,741
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	$ 773,200	$ 687,300	$ 2,167,100	$ 2,124,700
Concentration risk percentage	91.10%	90.90%	91.10%	91.50%
Customer Concentration Risk | Sales Revenue, Services, Net | Underground facility locating
Concentration Risk
Contract revenues	$ 48,800	$ 48,400	$ 142,900	$ 138,000
Concentration risk percentage	5.80%	6.40%	6.00%	5.90%
Customer Concentration Risk | Sales Revenue, Services, Net | Electrical and gas utilities and other
Concentration Risk
Contract revenues	$ 26,200	$ 20,500	$ 69,100	$ 60,000
Concentration risk percentage	3.10%	2.70%	2.90%	2.60%
Five Unnamed Customers | Customer Concentration Risk | Sales Revenue, Services, Net
Concentration Risk
Concentration risk percentage			78.30%	76.70%

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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