CASH, CASH EQUIVALENTS, RESTRICTED CASH AND MARKETABLE SECURITIES - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 147,963	$ 159,868
Unrealized Losses	(49)	(43)
Fair Value	147,914	159,825
U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	111,984	120,901
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	32,672	29,469
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value	3,258	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	138,758	137,916
Unrealized Losses	(39)	(24)
Fair Value	138,719	137,892
Short-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	102,826	98,989
Unrealized Losses	(37)	(21)
Fair Value	102,789	98,968
Short-term marketable securities | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	32,672	29,469
Unrealized Losses	0	0
Fair Value	32,672	29,469
Short-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,260	7,959
Unrealized Losses	(2)	(3)
Fair Value	3,258	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	9,205	21,952
Unrealized Losses	(10)	(19)
Fair Value	9,195	21,933
Long-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,205	21,952
Unrealized Losses	(10)	(19)
Fair Value	$ 9,195	$ 21,933