CASH, CASH EQUIVALENTS, AND INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2013	Mar. 31, 2013
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	$ 268,229	$ 232,704	$ 245,980	$ 228,776
Short-term investments (due in 1 year or less)	90,290	102,717
Long-term investments (due in 1 to 3 years)	111,720	100,342
Total cash, cash equivalents and investments measured at fair value, amortized cost	469,904	435,516
Total cash, cash equivalents and investments measured at fair value, gross unrealized gains	393	276
Total cash, cash equivalents and investments measured at fair value, gross unrealized losses	(58)	(29)
Total cash, cash equivalents and investments measured at fair value, fair value	470,239	435,763
Cash [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	263,730	232,704
Level 1 [Member] | Mutual Funds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale Securities, amortized cost basis	3,998	1,779
Available-for-sale Securities, gross unrealized gains	104	31
Available-for-sale Securities, gross unrealized losses	(21)	(3)
Available-for-sale Securities, fair value	4,081	1,807
Short-term investments (due in 1 year or less)	4,081	1,807
Long-term investments (due in 1 to 3 years)	0	0
Level 2 [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	4,499
Available-for-sale Securities, amortized cost basis	202,176	201,033
Available-for-sale Securities, gross unrealized gains	289	245
Available-for-sale Securities, gross unrealized losses	(37)	(26)
Available-for-sale Securities, fair value	202,428	201,252
Short-term investments (due in 1 year or less)	86,209	100,910
Long-term investments (due in 1 to 3 years)	111,720	100,342
Level 2 [Member] | Government Agency Securities [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale Securities, amortized cost basis	73,093	53,976
Available-for-sale Securities, gross unrealized gains	54	43
Available-for-sale Securities, gross unrealized losses	(19)	(9)
Available-for-sale Securities, fair value	73,128	54,010
Short-term investments (due in 1 year or less)	18,477	21,325
Long-term investments (due in 1 to 3 years)	54,651	32,685
Level 2 [Member] | Commercial Paper [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and cash equivalents	4,499
Available-for-sale Securities, amortized cost basis	32,581	47,766
Available-for-sale Securities, gross unrealized gains	4	7
Available-for-sale Securities, gross unrealized losses	(1)	0
Available-for-sale Securities, fair value	32,584	47,773
Short-term investments (due in 1 year or less)	28,085	47,773
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]
Available-for-sale Securities, amortized cost basis	96,502	98,289
Available-for-sale Securities, gross unrealized gains	231	195
Available-for-sale Securities, gross unrealized losses	(17)	(17)
Available-for-sale Securities, fair value	96,716	98,467
Short-term investments (due in 1 year or less)	39,647	30,810
Long-term investments (due in 1 to 3 years)	57,069	67,657
Level 2 [Member] | CDs [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale Securities, amortized cost basis		1,002
Available-for-sale Securities, gross unrealized gains		0
Available-for-sale Securities, gross unrealized losses		0
Available-for-sale Securities, fair value		1,002
Short-term investments (due in 1 year or less)		1,002
Long-term investments (due in 1 to 3 years)		$ 0