Fair Value of Financial Instruments (Details 1) - USD ($) $ in Thousands	Jul. 31, 2020	Jul. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 1,353,632	$ 1,258,361
Unrealized Gains	4,432	1,710
Unrealized Losses	(119)	(169)
Estimated Fair Value	1,357,945	1,259,902
U.S. Government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	242,153	55,904
Unrealized Gains	202	4
Unrealized Losses	(81)	(29)
Estimated Fair Value	242,274	55,879
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	222,578	239,333
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	222,578	239,333
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	474,646	666,087
Unrealized Gains	3,448	1,612
Unrealized Losses	(38)	(111)
Estimated Fair Value	478,056	667,588
U.S. Government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	68,332	130,530
Unrealized Gains	476	94
Unrealized Losses	0	(29)
Estimated Fair Value	68,808	130,595
Asset-backed Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	58,564
Unrealized Gains	306
Unrealized Losses	0
Estimated Fair Value	58,870
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	56,296	50,796
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	56,296	50,796
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	231,063	115,711
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	$ 231,063	$ 115,711