CASH, CASH EQUIVALENTS, AND INVESTMENTS (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	$ 242,461	$ 235,266	$ 219,091	$ 276,850
Short-term investments (due in 1 year or less)	177,442	160,051
Long-term investments (due in 1 to 3 years)	134,951	145,623
Total cash, cash equivalents and investments measured at fair value, amortized cost	555,214	541,303
Total cash, cash equivalents and investments measured at fair value, gross unrealized gains	191	311
Total cash, cash equivalents and investments measured at fair value, gross unrealized losses	(551)	(674)
Total cash, cash equivalents and investments measured at fair value, fair value	554,854	540,940
Cash [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	242,461	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	37,580	35,076
Available-for-sale Securities, gross unrealized gains	177	53
Available-for-sale Securities, gross unrealized losses	(138)	(557)
Available-for-sale Securities, fair value	37,619	34,572
Short-term investments (due in 1 year or less)	25,569	22,502
Long-term investments (due in 1 to 3 years)	12,050	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	11,970	10,025
Available-for-sale Securities, gross unrealized gains	177	32
Available-for-sale Securities, gross unrealized losses	(97)	(548)
Available-for-sale Securities, fair value	12,050	9,509
Short-term investments (due in 1 year or less)	12,050	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	25,610	25,051
Available-for-sale Securities, gross unrealized gains	0	21
Available-for-sale Securities, gross unrealized losses	(41)	(9)
Available-for-sale Securities, fair value	25,569	25,063
Short-term investments (due in 1 year or less)	13,519	12,993
Long-term investments (due in 1 to 3 years)	12,050	12,070
Level 2 [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	2,666
Available-for-sale Securities, amortized cost basis	275,173	273,627
Available-for-sale Securities, gross unrealized gains	14	258
Available-for-sale Securities, gross unrealized losses	(413)	(117)
Available-for-sale Securities, fair value	274,774	273,768
Short-term investments (due in 1 year or less)	151,873	137,549
Long-term investments (due in 1 to 3 years)	122,901	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	59,332	72,698
Available-for-sale Securities, gross unrealized gains	6	24
Available-for-sale Securities, gross unrealized losses	(144)	(20)
Available-for-sale Securities, fair value	59,194	72,702
Short-term investments (due in 1 year or less)	15,226	10,521
Long-term investments (due in 1 to 3 years)	43,968	62,181
Level 2 [Member] | Commercial Paper [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	0	650
Available-for-sale Securities, amortized cost basis	49,904	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	49,904	37,628
Short-term investments (due in 1 year or less)	49,904	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	144,291	147,662
Available-for-sale Securities, gross unrealized gains	8	234
Available-for-sale Securities, gross unrealized losses	(269)	(97)
Available-for-sale Securities, fair value	144,030	147,799
Short-term investments (due in 1 year or less)	68,804	77,115
Long-term investments (due in 1 to 3 years)	75,226	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	21,646	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	21,646	15,639
Short-term investments (due in 1 year or less)	17,939	12,935
Long-term investments (due in 1 to 3 years)	$ 3,707	$ 2,704