CASH, CASH EQUIVALENTS AND INVESTMENTS (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	$ 235,266	$ 276,850	$ 232,704	$ 228,776
Short-term investments (due in 1 year or less)	160,051	97,859
Long-term investments (due in 1 to 3 years)	145,623	107,590
Total cash, cash equivalents and investments measured at fair value, amortized cost	541,303	481,956
Total cash, cash equivalents and investments measured at fair value, gross unrealized gain	311	393
Total cash, cash equivalents and investments measured at fair value, gross unrealized loss	(674)	(50)
Total cash, cash equivalents and investments measured at fair value, fair value	540,940	482,299
Level 1
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0
Available-for-sale Securities, amortized cost basis	35,076
Available-for-sale Securities, gross unrealized gains	53
Available-for-sale Securities, gross unrealized losses	(557)
Available-for-sale Securities, fair value	34,572
Short-term investments (due in 1 year or less)	22,502
Long-term investments (due in 1 to 3 years)	12,070
Level 2
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	2,666	3,500
Available-for-sale Securities, amortized cost basis	273,627	203,208
Available-for-sale Securities, gross unrealized gains	258	246
Available-for-sale Securities, gross unrealized losses	(117)	(25)
Available-for-sale Securities, fair value	273,768	203,429
Short-term investments (due in 1 year or less)	137,549	92,339
Long-term investments (due in 1 to 3 years)	133,553	107,590
Cash
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	232,600	273,350
Mutual Funds | Level 1
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	10,025	5,398
Available-for-sale Securities, gross unrealized gains	32	147
Available-for-sale Securities, gross unrealized losses	(548)	(25)
Available-for-sale Securities, fair value	9,509	5,520
Short-term investments (due in 1 year or less)	9,509	5,520
Long-term investments (due in 1 to 3 years)	0	0
US Treasury Notes | Level 1
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0
Available-for-sale Securities, amortized cost basis	25,051
Available-for-sale Securities, gross unrealized gains	21
Available-for-sale Securities, gross unrealized losses	(9)
Available-for-sale Securities, fair value	25,063
Short-term investments (due in 1 year or less)	12,993
Long-term investments (due in 1 to 3 years)	12,070
Government Agency Securities | Level 2
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	72,698	89,875
Available-for-sale Securities, gross unrealized gains	24	37
Available-for-sale Securities, gross unrealized losses	(20)	(22)
Available-for-sale Securities, fair value	72,702	89,890
Short-term investments (due in 1 year or less)	10,521	43,024
Long-term investments (due in 1 to 3 years)	62,181	46,866
Commercial Paper-not included in Cash and Cash Equivalents | Level 2
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale Securities, amortized cost basis	37,628	17,574
Available-for-sale Securities, gross unrealized gains	0	10
Available-for-sale Securities, gross unrealized losses	0	0
Available-for-sale Securities, fair value	37,628	17,584
Short-term investments (due in 1 year or less)	36,978	14,084
Long-term investments (due in 1 to 3 years)	0	0
Commercial Paper | Level 2
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	650	3,500
Corporate Bonds | Level 2
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	2,016	0
Available-for-sale Securities, amortized cost basis	147,662	95,759
Available-for-sale Securities, gross unrealized gains	234	199
Available-for-sale Securities, gross unrealized losses	(97)	(3)
Available-for-sale Securities, fair value	147,799	95,955
Short-term investments (due in 1 year or less)	77,115	35,231
Long-term investments (due in 1 to 3 years)	68,668	$ 60,724
Certificates of Deposits (CDs) | Level 2
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0
Available-for-sale Securities, amortized cost basis	15,639
Available-for-sale Securities, gross unrealized gains	0
Available-for-sale Securities, gross unrealized losses	0
Available-for-sale Securities, fair value	15,639
Short-term investments (due in 1 year or less)	12,935
Long-term investments (due in 1 to 3 years)	$ 2,704