Goodwill and Intangible Assets (Details) (USD $)	12 Months Ended
	Jul. 27, 2013	Jul. 28, 2012	Jul. 30, 2011	Dec. 03, 2012
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Goodwill	$ 463,577,000	$ 370,616,000	$ 370,616,000
Accumulated impairment losses	(195,767,000)	(195,767,000)	(195,767,000)
Goodwill	267,810,000	174,849,000	174,849,000	87,900,000
Goodwill, Acquisition	92,961,000
Goodwill, impairment loss	0
Goodwill, period increase (decrease)	92,961,000
Carrying amount				90,600,000
Intangible Assets Gross Excluding Goodwill	193,082,000	96,855,000
Net Intangible Assets	125,275,000	49,773,000
Amortization expense for finite-lived intangible assets	20,700,000	6,500,000	6,800,000
UtiliQuest
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Goodwill		35,600,000
Indefinite-lived intangible assets	4,700,000	4,700,000
Margin of excess		20.00%
Customer Relationships
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangibles	75,400,000
Preliminary estimated useful life	15 years
Finite-lived intangible assets, weighted average remaining useful lives	12 years 4 months 24 days
Carrying amount	164,497,000	89,145,000
Accumulated amortization	56,219,000	45,852,000
Backlog
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangibles	15,300,000
Contract Backlog
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, weighted average remaining useful lives	2 years 3 months 18 days
Carrying amount	15,285,000	0
Accumulated amortization	9,433,000	0
Trade Names
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangibles	5,300,000
Preliminary estimated useful life	5 years	5 years
Finite-lived intangible assets, weighted average remaining useful lives	5 years 1 month 6 days
Carrying amount	8,200,000	2,860,000
Accumulated amortization	2,071,000	1,182,000
UtiliQuest trade name
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, weighted average remaining useful lives	0 years
Noncompete Agreements
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Intangibles	300,000
Finite-lived intangible assets, weighted average remaining useful lives	4 years 3 months 18 days
Carrying amount	400,000	150,000
Accumulated amortization	$ 84,000	$ 48,000
Minimum | Contract Backlog
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Preliminary estimated useful life	1 year
Maximum | Contract Backlog
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Preliminary estimated useful life	4 years
Goodwill [Member]
Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Fair Value Assumptions, Qualitiative Assessments, Reporting Units, Percentage	30.00%
Fair value assumptions, expected term	7 years