AVAILABLE-FOR-SALE-SECURITIES - FAIR VALUE AND GROSS REALIZED GAINS (LOSS) (Details) - USD ($) $ in Thousands	3 Months Ended
Jun. 30, 2018	Sep. 30, 2017
AVAILABLE FOR SALE SECURITIES [Abstract]
Available-for-sale securities	$ 124,455	$ 0
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	124,501
Debt Securities, Available-for-sale, Unrealized Gain	8
Debt Securities, Available-for-sale, Unrealized Loss	(54)
Available-for-sale securities	124,455	$ 0
Asset-backed Securities [Member]
AVAILABLE FOR SALE SECURITIES [Abstract]
Available-for-sale securities	13,901
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	13,900
Debt Securities, Available-for-sale, Unrealized Gain	1
Debt Securities, Available-for-sale, Unrealized Loss	0
Available-for-sale securities	13,901
Certificates of Deposit [Member]
AVAILABLE FOR SALE SECURITIES [Abstract]
Available-for-sale securities	2,442
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	2,439
Debt Securities, Available-for-sale, Unrealized Gain	3
Debt Securities, Available-for-sale, Unrealized Loss	0
Available-for-sale securities	2,442
Commercial Paper, Not Included with Cash and Cash Equivalents [Member]
AVAILABLE FOR SALE SECURITIES [Abstract]
Available-for-sale securities	7,754
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	7,756
Debt Securities, Available-for-sale, Unrealized Gain	0
Debt Securities, Available-for-sale, Unrealized Loss	(2)
Available-for-sale securities	7,754
Corporate Debt Securities [Member]
AVAILABLE FOR SALE SECURITIES [Abstract]
Available-for-sale securities	75,260
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	75,312
Debt Securities, Available-for-sale, Unrealized Gain	0
Debt Securities, Available-for-sale, Unrealized Loss	(52)
Available-for-sale securities	75,260
US Treasury Securities [Member]
AVAILABLE FOR SALE SECURITIES [Abstract]
Available-for-sale securities	25,098
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	25,094
Debt Securities, Available-for-sale, Unrealized Gain	4
Debt Securities, Available-for-sale, Unrealized Loss	0
Available-for-sale securities	$ 25,098

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount of unrealized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount of unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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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.

+ References

Reference 1: 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=109979856&loc=d3e26626-111562

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