CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Components of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Mar. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 138,279	$ 116,693
Unrealized Gains (Losses)	46	25
Fair Value	138,325	116,718
U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	116,280	91,757
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	15,987	14,581
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value	6,058	10,380
Short-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	90,738	75,207
Unrealized Gains (Losses)	45	27
Fair Value	90,783	75,234
Short-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	71,586	53,854
Unrealized Gains (Losses)	39	26
Fair Value	71,625	53,880
Short-term marketable securities | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,982	14,581
Unrealized Gains (Losses)	5	0
Fair Value	15,987	14,581
Short-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,170	6,772
Unrealized Gains (Losses)	1	1
Fair Value	3,171	6,773
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	47,541	41,486
Unrealized Gains (Losses)	1	(2)
Fair Value	47,542	41,484
Long-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	44,651	37,875
Unrealized Gains (Losses)	4	2
Fair Value	44,655	37,877
Long-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,890	3,611
Unrealized Gains (Losses)	(3)	(4)
Fair Value	$ 2,887	$ 3,607