CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Summary of Marketable Securities Classified as Short-term and Long-term (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Mar. 31, 2016
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	$ 159,868	$ 141,348
Unrealized Losses	(43)	16
Fair Value	159,825	141,364
U.S. government and municipal obligations
Cash, Cash Equivalents and Marketable Securities [Line Items]
Fair Value	120,901	123,328
Commercial paper
Cash, Cash Equivalents and Marketable Securities [Line Items]
Fair Value	29,469	16,172
Corporate bonds
Cash, Cash Equivalents and Marketable Securities [Line Items]
Fair Value	7,956	1,864
Certificates of deposit
Cash, Cash Equivalents and Marketable Securities [Line Items]
Fair Value	1,499
Short-term marketable securities
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	137,916	127,999
Unrealized Losses	(24)	4
Fair Value	137,892	128,003
Short-term marketable securities | U.S. government and municipal obligations
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	98,989	109,963
Unrealized Losses	(21)	4
Fair Value	98,968	109,967
Short-term marketable securities | Commercial paper
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	29,469	16,172
Unrealized Losses	0	0
Fair Value	29,469	16,172
Short-term marketable securities | Corporate bonds
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	7,959	1,864
Unrealized Losses	(3)	0
Fair Value	7,956	1,864
Short-term marketable securities | Certificates of deposit
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	1,499
Unrealized Losses	0
Fair Value	1,499
Long-term marketable securities
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	21,952	13,349
Unrealized Losses	(19)	12
Fair Value	21,933	13,361
Long-term marketable securities | U.S. government and municipal obligations
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	21,952	13,349
Unrealized Losses	(19)	12
Fair Value	$ 21,933	$ 13,361