CASH, CASH EQUIVALENTS, RESTRICTED CASH AND MARKETABLE SECURITIES - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 105,642	$ 78,003
Unrealized Losses	(5)	(62)
Fair Value	105,637	77,941
U.S. government and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Fair Value	46,015	42,186
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Fair Value	56,877	33,003
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value	2,745	2,752
Short-term marketable securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	105,642	78,003
Unrealized Losses	(5)	(62)
Fair Value	105,637	77,941
Short-term marketable securities | U.S. government and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	46,019	42,246
Unrealized Losses	(4)	(60)
Fair Value	46,015	42,186
Short-term marketable securities | Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	56,877	33,003
Unrealized Losses	0	0
Fair Value	56,877	33,003
Short-term marketable securities | Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,746	2,754
Unrealized Losses	(1)	(2)
Fair Value	2,745	2,752
Long-term marketable securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0	0
Unrealized Losses	0	0
Fair Value	$ 0	$ 0