CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Components of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Mar. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 93,538	$ 54,141
Unrealized Gains	27	20
Fair Value	93,565	54,161
U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	74,603	31,645
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	7,093	12,390
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value	9,810	5,166
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,059	4,960
Short-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	56,334	37,325
Unrealized Gains	9	13
Fair Value	56,343	37,338
Short-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	39,433	17,416
Unrealized Gains	5	11
Fair Value	39,438	17,427
Short-term marketable securities | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,093	12,390
Unrealized Gains	0	0
Fair Value	7,093	12,390
Short-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,749	2,559
Unrealized Gains	4	2
Fair Value	7,753	2,561
Short-term marketable securities | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,059	4,960
Unrealized Gains	0	0
Fair Value	2,059	4,960
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	37,204	16,816
Unrealized Gains	18	7
Fair Value	37,222	16,823
Long-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	35,147	14,211
Unrealized Gains	18	7
Fair Value	35,165	14,218
Long-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,057	2,605
Unrealized Gains	0	0
Fair Value	$ 2,057	$ 2,605