FAIR VALUE MEASUREMENTS - Schedule of Fair Value Measurements (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2019	Jun. 30, 2018
Non-current Assets
Total assets	$ 382,460	$ 298,658
Liabilities
Notes payable, at fair value		15,899
Level 1
Non-current Assets
Total assets	1,086	298,658
Liabilities
Notes payable, at fair value		0
Level 2
Non-current Assets
Total assets	381,374	0
Liabilities
Notes payable, at fair value		0
Level 3
Non-current Assets
Total assets	0	0
Liabilities
Notes payable, at fair value		15,899
U.S. treasury securities
Current Assets
Marketable securities	123,146	297,504
U.S. treasury securities \| Level 1
Current Assets
Marketable securities	0	297,504
U.S. treasury securities \| Level 2
Current Assets
Marketable securities	123,146	0
U.S. treasury securities \| Level 3
Current Assets
Marketable securities	0	0
Commercial paper
Current Assets
Marketable securities	110,478
Commercial paper \| Level 1
Current Assets
Marketable securities	0
Commercial paper \| Level 2
Current Assets
Marketable securities	110,478
Commercial paper \| Level 3
Current Assets
Marketable securities	0
Corporate bonds
Current Assets
Marketable securities	61,773
Non-current Assets
Marketable securities	32,465
Corporate bonds \| Level 1
Current Assets
Marketable securities	0
Non-current Assets
Marketable securities	0
Corporate bonds \| Level 2
Current Assets
Marketable securities	61,773
Non-current Assets
Marketable securities	32,465
Corporate bonds \| Level 3
Current Assets
Marketable securities	0
Non-current Assets
Marketable securities	0
Asset-backed securities
Current Assets
Marketable securities	30,759
Non-current Assets
Marketable securities	22,753
Asset-backed securities \| Level 1
Current Assets
Marketable securities	0
Non-current Assets
Marketable securities	0
Asset-backed securities \| Level 2
Current Assets
Marketable securities	30,759
Non-current Assets
Marketable securities	22,753
Asset-backed securities \| Level 3
Current Assets
Marketable securities	0
Non-current Assets
Marketable securities	0
Mutual fund securities
Current Assets
Marketable securities	296	235
Non-current Assets
Marketable securities	790	919
Mutual fund securities \| Level 1
Current Assets
Marketable securities	296	235
Non-current Assets
Marketable securities	790	919
Mutual fund securities \| Level 2
Current Assets
Marketable securities	0
Non-current Assets
Marketable securities	0	0
Mutual fund securities \| Level 3
Current Assets
Marketable securities	0	0
Non-current Assets
Marketable securities	$ 0	$ 0

Current Assets, Fair Value Disclosure [Abstract]

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Noncurrent Assets, Fair Value Disclosure [Abstract]

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
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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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Fair value portion of notes payable.

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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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