CASH, CASH EQUIVALENTS, RESTRICTED CASH AND MARKETABLE SECURITIES - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 89,384	$ 77,339
Unrealized Gains	57	17
Fair Value	89,441	77,356
U.S. government and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Fair Value	49,219	27,622
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Fair Value	37,553	48,722
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value	2,669	1,012
Short-term marketable securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	84,317	76,332
Unrealized Gains	37	12
Fair Value	84,354	76,344
Short-term marketable securities \| U.S. government and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	44,101	27,610
Unrealized Gains	31	12
Fair Value	44,132	27,622
Short-term marketable securities \| Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	37,553	48,722
Unrealized Gains	0	0
Fair Value	37,553	48,722
Short-term marketable securities \| Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,663
Unrealized Gains	6
Fair Value	2,669
Long-term marketable securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,067	1,007
Unrealized Gains	20	5
Fair Value	5,087	1,012
Long-term marketable securities \| U.S. government and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,067
Unrealized Gains	20
Fair Value	$ 5,087
Long-term marketable securities \| Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		1,007
Unrealized Gains		5
Fair Value		$ 1,012

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=118939692&loc=d3e27161-111563

Reference 2: 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

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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).

+ 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://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

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-Name Accounting Standards Codification
-Topic 320
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-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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

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