CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Summary of Marketable Securities Classified as Short-term and Long-term (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Mar. 31, 2015
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	$ 141,348	$ 159,951
Unrealized Gains (Losses)	16	13
Fair Value	141,364	159,964
U.S. government and municipal obligations
Cash, Cash Equivalents and Marketable Securities [Line Items]
Fair Value	123,328	145,345
Commercial paper
Cash, Cash Equivalents and Marketable Securities [Line Items]
Fair Value	16,172	5,095
Corporate bonds
Cash, Cash Equivalents and Marketable Securities [Line Items]
Fair Value	1,864	9,524
Short-term marketable securities
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	127,999	101,388
Unrealized Gains (Losses)	4	4
Fair Value	128,003	101,392
Short-term marketable securities | U.S. government and municipal obligations
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	109,963	88,651
Unrealized Gains (Losses)	4	3
Fair Value	109,967	88,654
Short-term marketable securities | Commercial paper
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	16,172	5,093
Unrealized Gains (Losses)	0	2
Fair Value	16,172	5,095
Short-term marketable securities | Corporate bonds
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	1,864	7,644
Unrealized Gains (Losses)	0	(1)
Fair Value	1,864	7,643
Long-term marketable securities
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	13,349	58,563
Unrealized Gains (Losses)	12	9
Fair Value	13,361	58,572
Long-term marketable securities | U.S. government and municipal obligations
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	13,349	56,683
Unrealized Gains (Losses)	12	8
Fair Value	13,361	56,691
Long-term marketable securities | Corporate bonds
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	0	1,880
Unrealized Gains (Losses)	0	1
Fair Value	$ 0	$ 1,881