CASH, CASH EQUIVALENTS, RESTRICTED CASH AND MARKETABLE SECURITIES - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Mar. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 62,694	$ 77,339
Unrealized Gains	65	17
Fair Value	62,759	77,356
Short-term marketable securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	55,091	76,332
Unrealized Gains	38	12
Fair Value	55,129	76,344
Short-term marketable securities | U.S. government and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	25,621	27,610
Unrealized Gains	29	12
Fair Value	25,650	27,622
Short-term marketable securities | Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	25,289	48,722
Unrealized Gains	0	0
Fair Value	25,289	48,722
Short-term marketable securities | Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4,181
Unrealized Gains	9
Fair Value	4,190
Long-term marketable securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,603	1,007
Unrealized Gains	27	5
Fair Value	7,630	1,012
Long-term marketable securities | U.S. government and municipal obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,603
Unrealized Gains	27
Fair Value	$ 7,630
Long-term marketable securities | Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		1,007
Unrealized Gains		5
Fair Value		$ 1,012