Income Taxes - Income Tax Reconciliation (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jan. 27, 2018	Jan. 28, 2017	Jul. 29, 2017	Jul. 30, 2016	Jul. 25, 2015
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Amount			$ 6,000	$ 4,500	$ 4,000
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount			1,300	2,500	2,800
Statutory rate applied to pre-tax income	$ 15,334		87,649	72,214	47,454
State taxes, net of federal tax benefit	1,406		9,868	7,398	5,159
Tax Reform and related effects	(32,249)		0	0	0
Federal benefit of vesting and exercise of share-based awards	(7,067)		0	0	0
Non-deductible and non-taxable items, net	1,585		(4,686)	(2,013)	(1,220)
Change in accruals for uncertain tax positions	250		632	113	(74)
Tax credits	(1,596)		0	0	0
Other items, net	52		(255)	(125)	(59)
Total provision for income taxes	$ (22,285)	$ 44,332	$ 93,208	$ 77,587	$ 51,260