CASH, CASH EQUIVALENTS, RESTRICTED CASH AND MARKETABLE SECURITIES - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Mar. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 51,173	$ 159,868
Unrealized Losses	(91)	(43)
Fair Value	51,082	159,825
U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	45,070	120,901
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	5,007	29,469
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,005	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	47,970	137,916
Unrealized Losses	(75)	(24)
Fair Value	47,895	137,892
Short-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	41,957	98,989
Unrealized Losses	(74)	(21)
Fair Value	41,883	98,968
Short-term marketable securities | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,007	29,469
Unrealized Losses	0	0
Fair Value	5,007	29,469
Short-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,006	7,959
Unrealized Losses	(1)	(3)
Fair Value	1,005	7,956
Short-term marketable securities | Certificate of deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,499
Unrealized Losses		0
Fair Value		1,499
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,203	21,952
Unrealized Losses	(16)	(19)
Fair Value	3,187	21,933
Long-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,203	21,952
Unrealized Losses	(16)	(19)
Fair Value	$ 3,187	$ 21,933