CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Mar. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 132,148	$ 141,348
Unrealized Gains (Losses)	(72)	16
Fair Value	132,076	141,364
U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	106,240	123,328
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	21,153	16,172
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value	4,683	1,864
Short-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	114,905	127,999
Unrealized Gains (Losses)	(35)	4
Fair Value	114,870	128,003
Short-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	89,067	109,963
Unrealized Gains (Losses)	(33)	4
Fair Value	89,034	109,967
Short-term marketable securities | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,153	16,172
Unrealized Gains (Losses)	0	0
Fair Value	21,153	16,172
Short-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,685	1,864
Unrealized Gains (Losses)	(2)	0
Fair Value	4,683	1,864
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,243	13,349
Unrealized Gains (Losses)	(37)	12
Fair Value	17,206	13,361
Long-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,243	13,349
Unrealized Gains (Losses)	(37)	12
Fair Value	$ 17,206	$ 13,361