CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Summary of Marketable Securities Classified as Short-term and Long-term (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	$ 78,003	$ 159,868
Unrealized Losses	(62)	(43)
Fair Value	77,941	159,825
U.S. government and municipal obligations
Cash, Cash Equivalents and Marketable Securities [Line Items]
Fair Value	42,186	120,901
Commercial paper
Cash, Cash Equivalents and Marketable Securities [Line Items]
Fair Value	33,003	29,469
Corporate bonds
Cash, Cash Equivalents and Marketable Securities [Line Items]
Fair Value	2,752	7,956
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	78,003	137,916
Unrealized Losses	(62)	(24)
Fair Value	77,941	137,892
Short-term marketable securities | U.S. government and municipal obligations
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	42,246	98,989
Unrealized Losses	(60)	(21)
Fair Value	42,186	98,968
Short-term marketable securities | Commercial paper
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	33,003	29,469
Unrealized Losses	0	0
Fair Value	33,003	29,469
Short-term marketable securities | Corporate bonds
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost	2,754	7,959
Unrealized Losses	(2)	(3)
Fair Value	2,752	7,956
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	0	21,952
Unrealized Losses	0	(19)
Fair Value	$ 0	21,933
Long-term marketable securities | U.S. government and municipal obligations
Cash, Cash Equivalents and Marketable Securities [Line Items]
Amortized Cost		21,952
Unrealized Losses		(19)
Fair Value		$ 21,933