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Income Taxes - Narratives (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jan. 27, 2018	Jan. 26, 2019	Jul. 29, 2017	Jul. 30, 2016	Jul. 25, 2015
Income Tax Contingency [Line Items]
Tax Cuts and Jobs Act of 2017, adjustment to income tax liability	$ 32,200
Effective tax rate	33.00%
Unrecognized tax benefits	$ 3,322	$ 3,786	$ 3,072	$ 2,440	$ 2,327
Payment of interest and penalties accrued	1,200	1,400
Tax benefit from exercise of stock options	7,800
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Amount			6,000	4,500
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount			1,300	2,500
Effective Income Tax Rate Reconciliation, Tax Credit, Amount	$ 1,596	$ 1,835	0	0
Non deductible ana non taxable item
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Tax Credit, Amount			$ 1,000	$ 700

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Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Deferred Tax Liability, Provisional Income Tax Benefit

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of the difference between reported income tax expense (benefit) and the expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to deduction for qualified production activity.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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