Fair Value of Financial Instruments (Details 1) - USD ($) $ in Thousands	Apr. 30, 2020	Jul. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 1,269,453	$ 1,258,361
Unrealized Gains	4,000	1,710
Unrealized Losses	(687)	(169)
Total	1,272,766	1,259,902
U.S. Government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	133,556	55,904
Unrealized Gains	171	4
Unrealized Losses	(107)	(29)
Total	133,620	55,879
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	156,729	239,333
Unrealized Gains	0	0
Unrealized Losses	0	0
Total	156,729	239,333
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	609,810	666,087
Unrealized Gains	2,800	1,612
Unrealized Losses	(561)	(111)
Total	612,049	667,588
U.S. Government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	78,138	130,530
Unrealized Gains	733	94
Unrealized Losses	0	(29)
Total	78,871	130,595
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	60,450
Unrealized Gains	292
Unrealized Losses	(18)
Total	60,724
Foreign government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	10,867
Unrealized Gains	4
Unrealized Losses	(1)
Total	10,870
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	37,645	50,796
Unrealized Gains	0	0
Unrealized Losses	0	0
Total	37,645	50,796
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	182,258	115,711
Unrealized Gains	0	0
Unrealized Losses	0	0
Total	$ 182,258	$ 115,711