Fair Value of Financial Instruments (Details 1) - USD ($) $ in Thousands	Jan. 31, 2020	Jul. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 1,268,711	$ 1,258,361
Unrealized Gains	2,741	1,710
Unrealized Losses	(22)	(169)
Total	1,271,430	1,259,902
U.S. Government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	59,083	55,904
Unrealized Gains	67	4
Unrealized Losses	(5)	(29)
Total	59,145	55,879
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	206,291	239,333
Unrealized Gains	0	0
Unrealized Losses	0	0
Total	206,291	239,333
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	653,011	666,087
Unrealized Gains	2,275	1,612
Unrealized Losses	(17)	(111)
Total	655,269	667,588
U.S. Government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	142,113	130,530
Unrealized Gains	231	94
Unrealized Losses	0	(29)
Total	142,344	130,595
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	60,342
Unrealized Gains	164
Unrealized Losses	0
Total	60,506
Foreign government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	10,870
Unrealized Gains	4
Unrealized Losses	0
Total	10,874
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	43,243	50,796
Unrealized Gains	0	0
Unrealized Losses	0	0
Total	43,243	50,796
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	93,758	115,711
Unrealized Gains	0	0
Unrealized Losses	0	0
Total	$ 93,758	$ 115,711