CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Mar. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 145,766	$ 159,951
Unrealized Gains (Losses)	(54)	13
Fair Value	145,712	159,964
U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	128,858	145,345
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	12,970	5,095
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value	3,885	9,524
Short-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	127,773	101,388
Unrealized Gains (Losses)	(22)	4
Fair Value	127,751	101,392
Short-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	110,917	88,651
Unrealized Gains (Losses)	(21)	3
Fair Value	110,896	88,654
Short-term marketable securities | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,970	5,093
Unrealized Gains (Losses)	0	2
Fair Value	12,970	5,095
Short-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,886	7,644
Unrealized Gains (Losses)	(1)	(1)
Fair Value	3,885	7,643
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,993	58,563
Unrealized Gains (Losses)	(32)	9
Fair Value	17,961	58,572
Long-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,993	56,683
Unrealized Gains (Losses)	(32)	8
Fair Value	$ 17,961	56,691
Long-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,880
Unrealized Gains (Losses)		1
Fair Value		$ 1,881