FAIR VALUE MEASUREMENTS - Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2019	Jul. 31, 2018
Financial Assets:
Short-term investments:	$ 495,633	$ 628,328
Recurring
Financial Assets:
Total measured at fair value	675,779	752,894
Cash	264,973	181,409
Total cash, cash equivalents and short-term investments	940,752	934,303
Recurring \| Commitments
Financial Liabilities:
Convertible preferred stock warrant liability		1,872
Recurring \| Corporate bonds
Financial Assets:
Short-term investments:	355,259	448,458
Recurring \| Commercial paper
Financial Assets:
Short-term investments:	96,214	120,772
Recurring \| U.S. government securities
Financial Assets:
Short-term investments:	44,160	59,098
Recurring \| Money market funds
Financial Assets:
Cash equivalents:	61,373	41,763
Recurring \| Commercial paper
Financial Assets:
Cash equivalents:	118,773	77,818
Recurring \| U.S. government securities
Financial Assets:
Cash equivalents:		4,985
Recurring \| Level I
Financial Assets:
Total measured at fair value	61,373	41,763
Recurring \| Level I \| Commitments
Financial Liabilities:
Convertible preferred stock warrant liability		0
Recurring \| Level I \| Corporate bonds
Financial Assets:
Short-term investments:	0	0
Recurring \| Level I \| Commercial paper
Financial Assets:
Short-term investments:	0	0
Recurring \| Level I \| U.S. government securities
Financial Assets:
Short-term investments:	0	0
Recurring \| Level I \| Money market funds
Financial Assets:
Cash equivalents:	61,373	41,763
Recurring \| Level I \| Commercial paper
Financial Assets:
Cash equivalents:	0	0
Recurring \| Level I \| U.S. government securities
Financial Assets:
Cash equivalents:		0
Recurring \| Level II
Financial Assets:
Total measured at fair value	614,406	711,131
Recurring \| Level II \| Commitments
Financial Liabilities:
Convertible preferred stock warrant liability		0
Recurring \| Level II \| Corporate bonds
Financial Assets:
Short-term investments:	355,259	448,458
Recurring \| Level II \| Commercial paper
Financial Assets:
Short-term investments:	96,214	120,772
Recurring \| Level II \| U.S. government securities
Financial Assets:
Short-term investments:	44,160	59,098
Recurring \| Level II \| Money market funds
Financial Assets:
Cash equivalents:	0	0
Recurring \| Level II \| Commercial paper
Financial Assets:
Cash equivalents:	118,773	77,818
Recurring \| Level II \| U.S. government securities
Financial Assets:
Cash equivalents:		4,985
Recurring \| Level III
Financial Assets:
Total measured at fair value	0	0
Recurring \| Level III \| Commitments
Financial Liabilities:
Convertible preferred stock warrant liability		1,872
Recurring \| Level III \| Corporate bonds
Financial Assets:
Short-term investments:	0	0
Recurring \| Level III \| Commercial paper
Financial Assets:
Short-term investments:	0	0
Recurring \| Level III \| U.S. government securities
Financial Assets:
Short-term investments:	0	0
Recurring \| Level III \| Money market funds
Financial Assets:
Cash equivalents:	0	0
Recurring \| Level III \| Commercial paper
Financial Assets:
Cash equivalents:	$ 0	0
Recurring \| Level III \| U.S. government securities
Financial Assets:
Cash equivalents:		$ 0

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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