CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Mar. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 107,995	$ 141,348
Unrealized Gains (Losses)	(23)	16
Fair Value	107,972	141,364
U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	86,907	123,328
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	21,065	16,172
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value		1,864
Short-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99,314	127,999
Unrealized Gains (Losses)	(17)	4
Fair Value	99,297	128,003
Short-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	78,249	109,963
Unrealized Gains (Losses)	(17)	4
Fair Value	78,232	109,967
Short-term marketable securities | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,065	16,172
Unrealized Gains (Losses)	0	0
Fair Value	21,065	16,172
Short-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,864
Unrealized Gains (Losses)		0
Fair Value		1,864
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,681	13,349
Unrealized Gains (Losses)	(6)	12
Fair Value	8,675	13,361
Long-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,681	13,349
Unrealized Gains (Losses)	(6)	12
Fair Value	$ 8,675	$ 13,361