Fair Value of Financial Instruments (Details 1) - USD ($) $ in Thousands	Oct. 31, 2020	Jul. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 1,337,279	$ 1,353,632
Unrealized Gains	2,918	4,432
Unrealized Losses	(97)	(119)
Total	1,340,100	1,357,945
U.S. Government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	209,058	242,153
Unrealized Gains	132	202
Unrealized Losses	(74)	(81)
Total	209,116	242,274
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	225,521	222,578
Unrealized Gains	0	0
Unrealized Losses	0	0
Total	225,521	222,578
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	446,845	474,646
Unrealized Gains	2,297	3,448
Unrealized Losses	(12)	(38)
Total	449,130	478,056
U.S. Government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	154,795	68,332
Unrealized Gains	339	476
Unrealized Losses	(8)	0
Total	155,126	68,808
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	47,369	58,564
Unrealized Gains	149	306
Unrealized Losses	0	0
Total	47,518	58,870
Foreign government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	7,474
Unrealized Gains	1
Unrealized Losses	(3)
Total	7,472
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	73,148	56,296
Unrealized Gains	0	0
Unrealized Losses	0	0
Total	73,148	56,296
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	173,069	231,063
Unrealized Gains	0	0
Unrealized Losses	0	0
Total	$ 173,069	$ 231,063