Goodwill and Intangible Assets (Details) (USD $)	3 Months Ended
	Oct. 27, 2012	Oct. 29, 2011	Jul. 28, 2012
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Goodwill	$ 174,849,000		$ 174,849,000
Intangible Assets Gross Excluding Goodwill	96,855,000		96,855,000
Net Intangible Assets	48,182,000		49,773,000
Amortization expense for finite-lived intangible assets	1,600,000	1,700,000
UtiliQuest
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Goodwill			35,600,000
Indefinite-Lived Intangible Assets (Excluding Goodwill)	4,700,000		4,700,000
Margin of Excess of Fair Value Over Carrying Value			30.00%
Customer Relationships
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	9 years 2 months 12 days
Carrying amount	89,145,000		89,145,000
Accumulated amortization	47,379,000		45,852,000
Trade Names
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	7 years 10 months 24 days
Carrying amount	2,860,000		2,860,000
Accumulated amortization	1,238,000		1,182,000
Noncompete Agreements
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	3 years 2 months 12 days
Carrying amount	150,000		150,000
Accumulated amortization	$ 56,000		$ 48,000