CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Summary of Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Mar. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 134,051	$ 116,693
Unrealized Gains (Losses)	(29)	25
Fair Value	134,022	116,718
U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	119,701	91,757
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	7,590	14,581
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value	6,731	10,380
Short-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	87,951	75,207
Unrealized Gains (Losses)	16	27
Fair Value	87,967	75,234
Short-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	74,483	53,854
Unrealized Gains (Losses)	15	26
Fair Value	74,498	53,880
Short-term marketable securities | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,586	14,581
Unrealized Gains (Losses)	4	0
Fair Value	7,590	14,581
Short-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,882	6,772
Unrealized Gains (Losses)	(3)	1
Fair Value	5,879	6,773
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	46,100	41,486
Unrealized Gains (Losses)	(45)	(2)
Fair Value	46,055	41,484
Long-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	45,248	37,875
Unrealized Gains (Losses)	(45)	2
Fair Value	45,203	37,877
Long-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	852	3,611
Unrealized Gains (Losses)	0	(4)
Fair Value	$ 852	$ 3,607