FAIR VALUE MEASUREMENTS - Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Jul. 31, 2018	Jul. 31, 2017
Financial Assets:
Short-term investments:	$ 628,328	$ 210,694
Recurring
Financial Assets:
Total measured at fair value	752,894	268,519
Cash	181,409	80,534
Total cash, cash equivalents and short-term investments	934,303	349,053
Recurring \| Warrant
Financial Liabilities:
Convertible preferred stock warrant liability	1,872	4,295
Recurring \| Corporate bonds
Financial Assets:
Short-term investments:	448,458	160,634
Recurring \| Commercial paper
Financial Assets:
Short-term investments:	120,772	36,084
Recurring \| US Government Debt Securities
Financial Assets:
Cash equivalents:	4,985
Short-term investments:	59,098	13,976
Recurring \| Money market funds
Financial Assets:
Cash equivalents:	41,763	34,784
Recurring \| Commercial paper
Financial Assets:
Cash equivalents:	77,818	23,041
Recurring \| Level I
Financial Assets:
Total measured at fair value	41,763	34,784
Recurring \| Level I \| Warrant
Financial Liabilities:
Convertible preferred stock warrant liability	0	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 \| US Government Debt Securities
Financial Assets:
Short-term investments:	0	0
Recurring \| Level I \| Money market funds
Financial Assets:
Cash equivalents:	41,763	34,784
Recurring \| Level I \| Commercial paper
Financial Assets:
Cash equivalents:	0	0
Recurring \| Level II
Financial Assets:
Total measured at fair value	711,131	233,735
Recurring \| Level II \| Warrant
Financial Liabilities:
Convertible preferred stock warrant liability	0	0
Recurring \| Level II \| Corporate bonds
Financial Assets:
Short-term investments:	448,458	160,634
Recurring \| Level II \| Commercial paper
Financial Assets:
Short-term investments:	120,772	36,084
Recurring \| Level II \| US Government Debt Securities
Financial Assets:
Cash equivalents:	4,985
Short-term investments:	59,098	13,976
Recurring \| Level II \| Money market funds
Financial Assets:
Cash equivalents:	0	0
Recurring \| Level II \| Commercial paper
Financial Assets:
Cash equivalents:	77,818	23,041
Recurring \| Level III
Financial Assets:
Total measured at fair value	0	0
Recurring \| Level III \| Warrant
Financial Liabilities:
Convertible preferred stock warrant liability	1,872	4,295
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 \| US Government Debt 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

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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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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Excludes cash and cash equivalents within disposal group and discontinued operation.

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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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