CASH, CASH EQUIVALENTS, RESTRICTED CASH AND MARKETABLE SECURITIES - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Mar. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 61,903	$ 159,868
Unrealized Gains (Losses)	(29)	(43)
Fair Value	61,874	159,825
U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	46,888	120,901
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	13,984	29,469
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,002	7,956
Certificate of deposits
Schedule of Available-for-sale Securities [Line Items]
Fair Value		1,499
Short-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	55,613	137,916
Unrealized Gains (Losses)	(31)	(24)
Fair Value	55,582	137,892
Short-term marketable securities \| U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	40,626	98,989
Unrealized Gains (Losses)	(30)	(21)
Fair Value	40,596	98,968
Short-term marketable securities \| Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,984	29,469
Unrealized Gains (Losses)	0	0
Fair Value	13,984	29,469
Short-term marketable securities \| Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,003	7,959
Unrealized Gains (Losses)	(1)	(3)
Fair Value	1,002	7,956
Short-term marketable securities \| Certificate of deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,499
Unrealized Gains (Losses)		0
Fair Value		1,499
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,290	21,952
Unrealized Gains (Losses)	2	(19)
Fair Value	6,292	21,933
Long-term marketable securities \| U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,290	21,952
Unrealized Gains (Losses)	2	(19)
Fair Value	$ 6,292	$ 21,933

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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