CASH, CASH EQUIVALENTS, AND INVESTMENTS (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Mar. 31, 2015
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	$ 227,473	$ 235,266	$ 475,379	$ 276,850
Short-term investments (due in 1 year or less)	171,899	160,051
Long-term investments (due in 1 to 3 years)	132,270	145,623
Total cash, cash equivalents and investments measured at fair value, amortized cost	531,405	541,303
Total cash, cash equivalents and investments measured at fair value, gross unrealized gains	659	311
Total cash, cash equivalents and investments measured at fair value, gross unrealized losses	(422)	(674)
Total cash, cash equivalents and investments measured at fair value, fair value	531,642	540,940
Cash [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	215,580	232,600
Level 1 [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	34,895	35,076
Available-for-sale Securities, gross unrealized gains	184	53
Available-for-sale Securities, gross unrealized losses	(362)	(557)
Available-for-sale Securities, fair value	34,717	34,572
Short-term investments (due in 1 year or less)	24,618	22,502
Long-term investments (due in 1 to 3 years)	10,099	12,070
Level 1 [Member] | Mutual Funds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	10,871	10,025
Available-for-sale Securities, gross unrealized gains	131	32
Available-for-sale Securities, gross unrealized losses	(362)	(548)
Available-for-sale Securities, fair value	10,640	9,509
Short-term investments (due in 1 year or less)	10,640	9,509
Long-term investments (due in 1 to 3 years)	0	0
Level 1 [Member] | US Treasury Notes [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	24,024	25,051
Available-for-sale Securities, gross unrealized gains	53	21
Available-for-sale Securities, gross unrealized losses	0	(9)
Available-for-sale Securities, fair value	24,077	25,063
Short-term investments (due in 1 year or less)	13,978	12,993
Long-term investments (due in 1 to 3 years)	10,099	12,070
Level 2 [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	11,893	2,666
Available-for-sale Securities, amortized cost basis	280,930	273,627
Available-for-sale Securities, gross unrealized gains	475	258
Available-for-sale Securities, gross unrealized losses	(60)	(117)
Available-for-sale Securities, fair value	281,345	273,768
Short-term investments (due in 1 year or less)	147,281	137,549
Long-term investments (due in 1 to 3 years)	122,171	133,553
Level 2 [Member] | Government Agency Securities [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	61,399	72,698
Available-for-sale Securities, gross unrealized gains	79	24
Available-for-sale Securities, gross unrealized losses	(3)	(20)
Available-for-sale Securities, fair value	61,475	72,702
Short-term investments (due in 1 year or less)	8,533	10,521
Long-term investments (due in 1 to 3 years)	52,942	62,181
Level 2 [Member] | Commercial Paper [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	11,893	650
Available-for-sale Securities, amortized cost basis	57,167	37,628
Available-for-sale Securities, gross unrealized gains	0	0
Available-for-sale Securities, gross unrealized losses	0	0
Available-for-sale Securities, fair value	57,167	37,628
Short-term investments (due in 1 year or less)	45,274	36,978
Long-term investments (due in 1 to 3 years)	0	0
Level 2 [Member] | Corporate Bonds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	2,016
Available-for-sale Securities, amortized cost basis	141,424	147,662
Available-for-sale Securities, gross unrealized gains	396	234
Available-for-sale Securities, gross unrealized losses	(57)	(97)
Available-for-sale Securities, fair value	141,763	147,799
Short-term investments (due in 1 year or less)	76,240	77,115
Long-term investments (due in 1 to 3 years)	65,523	68,668
Level 2 [Member] | Certificates of Deposit [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	20,940	15,639
Available-for-sale Securities, gross unrealized gains	0	0
Available-for-sale Securities, gross unrealized losses	0	0
Available-for-sale Securities, fair value	20,940	15,639
Short-term investments (due in 1 year or less)	17,234	12,935
Long-term investments (due in 1 to 3 years)	$ 3,706	$ 2,704