Basis of Presentation and Accounting Policies (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Jul. 30, 2016 USD ($) shares	Apr. 23, 2016 USD ($)	Jan. 23, 2016 USD ($)	Oct. 24, 2015 USD ($)	Jul. 25, 2015 USD ($)	Apr. 25, 2015 USD ($)	Jan. 24, 2015 USD ($)	Oct. 25, 2014 USD ($)	Jul. 29, 2017	Jul. 30, 2016 USD ($) segment shares	Jul. 25, 2015 USD ($)	Jul. 26, 2014
Segment Reporting Information [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant | shares	1,023,162									1,023,162
Capitalized Computer Software, Net	$ 23,000				$ 21,800					$ 23,000	$ 21,800
Revenues	789,159	$ 664,645	$ 559,470	$ 659,268	578,479	$ 492,363	$ 441,081	$ 510,389
Accrued Insurance	89,700				87,300					89,700	87,300
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred but Not Reported (IBNR) Claims, Amount	44,500				39,400					44,500	39,400
Accrued insurance claims	36,844				35,824					$ 36,844	35,824
Number of reportable segments | segment										1
Prepaid Expense and Other Assets	17,700				13,500					$ 17,700	13,500
Debt Issuance Costs, Net	6,400				6,700					6,400	6,700
Insurance recoveries/receivables related to accrued claims	5,700				9,500					5,700	9,500
Restricted cash	5,000				4,500					$ 5,000	4,500
Measurement period										12 months
Investments and other noncurrent assets	4,000				4,000					$ 4,000	$ 4,000
Fiscal period duration										371 days	364 days	364 days
Non-Current Other Assets
Segment Reporting Information [Line Items]
Insurance recoveries/receivables related to accrued claims					8,900						$ 8,900
Income taxes payable
Segment Reporting Information [Line Items]
Prior period reclassification adjustment											$ 8,900
Revenue Recognized Using Cost To Cost Percentage of Completion Method | Maximum
Segment Reporting Information [Line Items]
Contract revenues										5.00%	10.00%	10.00%
Stock Options
Segment Reporting Information [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period										4 years	4 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period										10 years	10 years
Performance RSUs
Segment Reporting Information [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period										3 years	3 years
Supplemental Shares
Segment Reporting Information [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period										3 years	3 years
RSUs
Segment Reporting Information [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period										4 years	4 years
Accounting Standards Update 2015-03 | Non-Current Other Assets
Segment Reporting Information [Line Items]
Debt Issuance Costs, Net	(1,200)				(4,900)					$ (1,200)	$ (4,900)
Accounting Standards Update 2015-03 | Long-term Debt
Segment Reporting Information [Line Items]
Debt Issuance Costs, Net	$ 1,200				$ 4,900					$ 1,200	$ 4,900
Scenario, Forecast
Segment Reporting Information [Line Items]
Fiscal period duration									364 days