CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Components of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Mar. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 64,508	$ 54,141
Unrealized Gains	24	20
Fair Value	64,532	54,161
U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	39,167	31,645
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	5,597	12,390
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value	17,109	5,166
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,659	4,960
Short-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	42,086	37,325
Unrealized Gains	8	13
Fair Value	42,094	37,338
Short-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	28,172	17,416
Unrealized Gains	3	11
Fair Value	28,175	17,427
Short-term marketable securities | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,597	12,390
Unrealized Gains	0	0
Fair Value	5,597	12,390
Short-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,658	2,559
Unrealized Gains	5	2
Fair Value	5,663	2,561
Short-term marketable securities | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,659	4,960
Unrealized Gains	0	0
Fair Value	2,659	4,960
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,422	16,816
Unrealized Gains	16	7
Fair Value	22,438	16,823
Long-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,984	14,211
Unrealized Gains	8	7
Fair Value	10,992	14,218
Long-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,438	2,605
Unrealized Gains	8	0
Fair Value	$ 11,446	$ 2,605