Goodwill and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 25, 2020	Jul. 27, 2019	Jul. 25, 2020	Jul. 27, 2019	Jan. 25, 2020
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Amortization of intangible assets	$ 5,200	$ 5,300	$ 10,400	$ 10,700
Intangible Assets, Gross (Excluding Goodwill)	327,267		327,267		$ 327,267
Accumulated Amortization	197,741		197,741		187,322
Intangible Assets, Net	129,526		129,526		139,945
UtiliQuest
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	4,700		4,700		4,700
Accumulated Amortization	0		0		0
Intangible Assets, Net	$ 4,700		4,700		4,700
Customer relationships
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Usesul life	9 years 9 months 18 days
Intangible Assets, Gross (Excluding Goodwill)	$ 312,017		312,017		312,017
Accumulated Amortization	188,601		188,601		178,411
Intangible Assets, Net	$ 123,416		123,416		133,606
Trade names
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Usesul life	7 years 10 months 24 days
Intangible Assets, Gross (Excluding Goodwill)	$ 10,350		10,350		10,350
Accumulated Amortization	8,941		8,941		8,732
Intangible Assets, Net	$ 1,409		1,409		1,618
Non-compete agreements
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Usesul life	1 month 6 days
Intangible Assets, Gross (Excluding Goodwill)	$ 200		200		200
Accumulated Amortization	199		199		179
Intangible Assets, Net	$ 1		$ 1		$ 21