CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Mar. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 123,995	$ 141,348
Unrealized Gains	57	16
Fair Value	124,052	141,364
U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value	97,338	123,328
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Fair Value	26,714	16,172
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Fair Value		1,864
Short-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	108,719	127,999
Unrealized Gains	24	4
Fair Value	108,743	128,003
Short-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	82,005	109,963
Unrealized Gains	24	4
Fair Value	82,029	109,967
Short-term marketable securities | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	26,714	16,172
Unrealized Gains	0	0
Fair Value	26,714	16,172
Short-term marketable securities | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,864
Unrealized Gains		0
Fair Value		1,864
Long-term marketable securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,276	13,349
Unrealized Gains	33	12
Fair Value	15,309	13,361
Long-term marketable securities | U.S. government and municipal obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,276	13,349
Unrealized Gains	33	12
Fair Value	$ 15,309	$ 13,361