CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Components of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 145,401	$ 116,693
Unrealized Gains (Losses)	69	25
Fair Value	145,470	116,718
U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	115,494	91,757
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	23,882	14,581
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value	6,094	10,380
Short-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	88,850	75,207
Unrealized Gains (Losses)	40	27
Fair Value	88,890	75,234
Short-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	61,764	53,854
Unrealized Gains (Losses)	37	26
Fair Value	61,801	53,880
Short-term marketable securities | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,881	14,581
Unrealized Gains (Losses)	1	0
Fair Value	23,882	14,581
Short-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,205	6,772
Unrealized Gains (Losses)	2	1
Fair Value	3,207	6,773
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	56,551	41,486
Unrealized Gains (Losses)	29	(2)
Fair Value	56,580	41,484
Long-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	53,663	37,875
Unrealized Gains (Losses)	30	2
Fair Value	53,693	37,877
Long-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,888	3,611
Unrealized Gains (Losses)	(1)	(4)
Fair Value	$ 2,887	$ 3,607