Acquisitions - Net Assets Acquired (Details) (USD $)	Jan. 25, 2014	Jul. 27, 2013	Dec. 03, 2012
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract [Abstract]
Cash and equivalents			$ 200,000
Accounts receivable, net			112,200,000
Costs and estimated earnings in excess of billings			61,500,000
Inventories			9,000,000
Other current assets			1,600,000
Property and equipment			33,300,000
Goodwill	267,810,000	267,810,000	87,900,000
Other assets			2,300,000
Total assets			398,600,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Accounts payable			42,100,000
Billings in excess of costs and estimated earnings			10,300,000
Accrued and other liabilities			27,100,000
Total liabilities			79,500,000
Net Assets Acquired			319,100,000
Order or Production Backlog
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract [Abstract]
Intangibles		15,300,000
Quanta Services, Inc. | Customer Relationships
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract [Abstract]
Intangibles		70,300,000
Quanta Services, Inc. | Trade Names
BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract [Abstract]
Intangibles		$ 5,000,000