Fair Value of Financial Instruments (Details 1) - USD ($) $ in Thousands	Oct. 31, 2019	Jul. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 1,264,299	$ 1,258,361
Unrealized Gains	2,931	1,710
Unrealized Losses	(12)	(169)
Total	1,267,218	1,259,902
U.S. Government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	85,668	55,904
Unrealized Gains	59	4
Unrealized Losses	(7)	(29)
Total	85,720	55,879
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	165,218	239,333
Unrealized Gains	0	0
Unrealized Losses	0	0
Total	165,218	239,333
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	651,550	666,087
Unrealized Gains	2,528	1,612
Unrealized Losses	(4)	(111)
Total	654,074	667,588
U.S. Government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	148,035	130,530
Unrealized Gains	279	94
Unrealized Losses	(1)	(29)
Total	148,313	130,595
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	60,244
Unrealized Gains	65
Unrealized Losses	0
Total	60,309
Foreign government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	14,975
Unrealized Gains	0
Unrealized Losses	0
Total	14,975
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	37,545	50,796
Unrealized Gains	0	0
Unrealized Losses	0	0
Total	37,545	50,796
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	101,064	115,711
Unrealized Gains	0	0
Unrealized Losses	0	0
Total	$ 101,064	$ 115,711