Financial Instruments - Gross Unrealized Losses and Fair Values (Details) - USD ($) $ in Thousands	Aug. 02, 2020	Jul. 31, 2019
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Fair Value, Less than 12 months	$ 6,305	$ 14,689
Unrealized Loss, Less than 12 Months	(6)	(4)
Fair Value, Greater than 12 months	0	1,000
Unrealized Loss, Greater than 12 months	0	0
Fair Value, Total	6,305	15,689
Unrealized Loss, Total	(6)	(4)
U.S. government treasury notes
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Fair Value, Less than 12 months		0
Unrealized Loss, Less than 12 Months		0
Fair Value, Greater than 12 months		1,000
Unrealized Loss, Greater than 12 months		0
Fair Value, Total		1,000
Unrealized Loss, Total		0
U.S. government agencies
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Fair Value, Less than 12 months	4,996	4,998
Unrealized Loss, Less than 12 Months	(4)	(3)
Fair Value, Greater than 12 months	0	0
Unrealized Loss, Greater than 12 months	0	0
Fair Value, Total	4,996	4,998
Unrealized Loss, Total	(4)	(3)
Corporate debt securities
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss [Abstract]
Fair Value, Less than 12 months	1,309	9,691
Unrealized Loss, Less than 12 Months	(2)	(1)
Fair Value, Greater than 12 months	0	0
Unrealized Loss, Greater than 12 months	0	0
Fair Value, Total	1,309	9,691
Unrealized Loss, Total	$ (2)	$ (1)