Fair Value of Financial Instruments (Details 3) - USD ($) $ in Thousands	Apr. 30, 2020	Jul. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than 12 Months	$ 981,006
12 Months or Greater	291,760
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]
Less than 12 Months	20,742
12 Months or Greater	112,878
Total	133,620	55,879
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than 12 Months	156,729
12 Months or Greater	0
Total	156,729	239,333
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than 12 Months	495,082
12 Months or Greater	116,967
Total	612,049	667,588
U.S. Government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than 12 Months	55,806
12 Months or Greater	23,065
Total	78,871	130,595
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than 12 Months	26,121
12 Months or Greater	34,603
Total	60,724
Foreign government bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than 12 Months	10,870
12 Months or Greater	0
Total	10,870
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than 12 Months	33,398
12 Months or Greater	4,247
Total	37,645	50,796
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Less than 12 Months	182,258
12 Months or Greater	0
Total	$ 182,258	$ 115,711