CASH, CASH EQUIVALENTS AND INVESTMENTS (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	$ 301,970	$ 235,266	$ 276,850	$ 232,704
Short-term investments (due in 1 year or less)	178,179	160,051
Long-term investments (due in 1 to 3 years)	127,176	145,623
Total cash, cash equivalents and investments measured at fair value, amortized cost	607,374	541,303
Total cash, cash equivalents and investments measured at fair value, gross unrealized gain	439	311
Total cash, cash equivalents and investments measured at fair value, gross unrealized loss	(488)	(674)
Total cash, cash equivalents and investments measured at fair value, fair value	607,325	540,940
Level 1
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	48,039	35,076
Available-for-sale Securities, gross unrealized gains	352	53
Available-for-sale Securities, gross unrealized losses	(100)	(557)
Available-for-sale Securities, fair value	48,291	34,572
Short-term investments (due in 1 year or less)	29,959	22,502
Long-term investments (due in 1 to 3 years)	18,332	12,070
Level 2
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	6,093	2,666
Available-for-sale Securities, amortized cost basis	263,458	273,627
Available-for-sale Securities, gross unrealized gains	87	258
Available-for-sale Securities, gross unrealized losses	(388)	(117)
Available-for-sale Securities, fair value	263,157	273,768
Short-term investments (due in 1 year or less)	148,220	137,549
Long-term investments (due in 1 to 3 years)	108,844	133,553
Cash
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	295,877	232,600
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	12,079	10,025
Available-for-sale Securities, gross unrealized gains	352	32
Available-for-sale Securities, gross unrealized losses	(32)	(548)
Available-for-sale Securities, fair value	12,399	9,509
Short-term investments (due in 1 year or less)	12,399	9,509
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	0
Available-for-sale Securities, amortized cost basis	35,960	25,051
Available-for-sale Securities, gross unrealized gains	0	21
Available-for-sale Securities, gross unrealized losses	(68)	(9)
Available-for-sale Securities, fair value	35,892	25,063
Short-term investments (due in 1 year or less)	17,560	12,993
Long-term investments (due in 1 to 3 years)	18,332	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	54,415	72,698
Available-for-sale Securities, gross unrealized gains	20	24
Available-for-sale Securities, gross unrealized losses	(164)	(20)
Available-for-sale Securities, fair value	54,271	72,702
Short-term investments (due in 1 year or less)	15,309	10,521
Long-term investments (due in 1 to 3 years)	38,962	62,181
Commercial Paper-not included in Cash and Cash Equivalents | Level 2
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	6,093	650
Available-for-sale Securities, amortized cost basis	47,152	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	47,152	37,628
Short-term investments (due in 1 year or less)	41,059	36,978
Long-term investments (due in 1 to 3 years)	0	0
Corporate Bonds | Level 2
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	2,016
Available-for-sale Securities, amortized cost basis	141,508	147,662
Available-for-sale Securities, gross unrealized gains	64	234
Available-for-sale Securities, gross unrealized losses	(224)	(97)
Available-for-sale Securities, fair value	141,348	147,799
Short-term investments (due in 1 year or less)	73,676	77,115
Long-term investments (due in 1 to 3 years)	67,672	68,668
Certificates of Deposits (CDs) | Level 2
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	0
Available-for-sale Securities, amortized cost basis	20,383	15,639
Available-for-sale Securities, gross unrealized gains	3	0
Available-for-sale Securities, gross unrealized losses	0	0
Available-for-sale Securities, fair value	20,386	15,639
Short-term investments (due in 1 year or less)	18,176	12,935
Long-term investments (due in 1 to 3 years)	$ 2,210	$ 2,704