FAIR VALUE MEASUREMENTS - Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Jan. 31, 2020	Jul. 31, 2019
Financial Assets:
Short-term investments:	$ 607,307	$ 512,156
Recurring
Financial Assets:
Total measured at fair value	646,317	778,270
Cash	172,683	130,564
Total cash, cash equivalents and short-term investments	819,000	908,834
Recurring \| Corporate bonds
Financial Assets:
Short-term investments:	395,673	354,549
Recurring \| Commercial paper
Financial Assets:
Short-term investments:	115,762	92,851
Recurring \| U.S. government securities
Financial Assets:
Short-term investments:	95,872	64,756
Recurring \| Money market funds
Financial Assets:
Cash equivalents:	29,792	33,156
Recurring \| Commercial paper
Financial Assets:
Cash equivalents:	3,498	103,029
Recurring \| U.S. government securities
Financial Assets:
Cash equivalents:	3,670	119,933
Recurring \| Corporate bonds
Financial Assets:
Cash equivalents:	2,050	9,996
Recurring \| Level I
Financial Assets:
Total measured at fair value	29,792	33,156
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:	29,792	33,156
Recurring \| Level I \| Commercial paper
Financial Assets:
Cash equivalents:	0	0
Recurring \| Level I \| U.S. government securities
Financial Assets:
Cash equivalents:	0	0
Recurring \| Level I \| Corporate bonds
Financial Assets:
Cash equivalents:	0	0
Recurring \| Level II
Financial Assets:
Total measured at fair value	616,525	745,114
Recurring \| Level II \| Corporate bonds
Financial Assets:
Short-term investments:	395,673	354,549
Recurring \| Level II \| Commercial paper
Financial Assets:
Short-term investments:	115,762	92,851
Recurring \| Level II \| U.S. government securities
Financial Assets:
Short-term investments:	95,872	64,756
Recurring \| Level II \| Money market funds
Financial Assets:
Cash equivalents:	0	0
Recurring \| Level II \| Commercial paper
Financial Assets:
Cash equivalents:	3,498	103,029
Recurring \| Level II \| U.S. government securities
Financial Assets:
Cash equivalents:	3,670	119,933
Recurring \| Level II \| Corporate bonds
Financial Assets:
Cash equivalents:	2,050	9,996
Recurring \| Level III
Financial Assets:
Total measured at fair value	0	0
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	0
Recurring \| Level III \| Corporate bonds
Financial Assets:
Cash equivalents:	$ 0	$ 0

No definition available.

Name:	us-gaap_AssetsFairValueDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26626-111562

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 45
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118262064&loc=SL116631418-115840

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 45
-Paragraph 21
-URI http://asc.fasb.org/extlink&oid=118262064&loc=SL116631419-115840

+ Details

Name:	us-gaap_Cash
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion 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. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

+ Details

Name:	us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_CashCashEquivalentsAndShortTermInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_InvestmentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CashAndCashEquivalentsAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CashAndCashEquivalentsAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CashAndCashEquivalentsAxis=us-gaap_USGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CashAndCashEquivalentsAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: