CASH, CASH EQUIVALENTS, AND INVESTMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	$ 244,455	$ 235,266	$ 304,836	$ 276,850
Short-term investments (due in 1 year or less)	178,485	160,051
Long-term investments (due in 1 to 3 years)	130,695	145,623
Total cash, cash equivalents and investments measured at fair value, amortized cost	553,302	541,303
Total cash, cash equivalents and investments measured at fair value, gross unrealized gains	467	311
Total cash, cash equivalents and investments measured at fair value, gross unrealized losses	(134)	(674)
Total cash, cash equivalents and investments measured at fair value, fair value	553,635	540,940
Cash [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	236,361	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	31,933	35,076
Available-for-sale Securities, gross unrealized gains	222	53
Available-for-sale Securities, gross unrealized losses	(57)	(557)
Available-for-sale Securities, fair value	32,098	34,572
Short-term investments (due in 1 year or less)	23,518	22,502
Long-term investments (due in 1 to 3 years)	8,580	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	11,399	10,025
Available-for-sale Securities, gross unrealized gains	198	32
Available-for-sale Securities, gross unrealized losses	(53)	(548)
Available-for-sale Securities, fair value	11,544	9,509
Short-term investments (due in 1 year or less)	11,544	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	20,534	25,051
Available-for-sale Securities, gross unrealized gains	24	21
Available-for-sale Securities, gross unrealized losses	(4)	(9)
Available-for-sale Securities, fair value	20,554	25,063
Short-term investments (due in 1 year or less)	11,974	12,993
Long-term investments (due in 1 to 3 years)	8,580	12,070
Level 2 [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	8,094	2,666
Available-for-sale Securities, amortized cost basis	285,008	273,627
Available-for-sale Securities, gross unrealized gains	245	258
Available-for-sale Securities, gross unrealized losses	(77)	(117)
Available-for-sale Securities, fair value	285,176	273,768
Short-term investments (due in 1 year or less)	154,967	137,549
Long-term investments (due in 1 to 3 years)	122,115	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	55,039	72,698
Available-for-sale Securities, gross unrealized gains	29	24
Available-for-sale Securities, gross unrealized losses	(11)	(20)
Available-for-sale Securities, fair value	55,057	72,702
Short-term investments (due in 1 year or less)	12,239	10,521
Long-term investments (due in 1 to 3 years)	42,818	62,181
Level 2 [Member] \| Commercial Paper [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	8,094	650
Available-for-sale Securities, amortized cost basis	58,506	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	58,506	37,628
Short-term investments (due in 1 year or less)	50,412	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	148,547	147,662
Available-for-sale Securities, gross unrealized gains	216	234
Available-for-sale Securities, gross unrealized losses	(66)	(97)
Available-for-sale Securities, fair value	148,697	147,799
Short-term investments (due in 1 year or less)	73,110	77,115
Long-term investments (due in 1 to 3 years)	75,587	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	22,916	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	22,916	15,639
Short-term investments (due in 1 year or less)	19,206	12,935
Long-term investments (due in 1 to 3 years)	$ 3,710	$ 2,704

Cash, Cash Equivalents, Short-term and Long-term Investments, Amortized Cost

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle).

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