CASH, CASH EQUIVALENTS AND INVESTMENTS (Details) (USD $) In Thousands	Jun. 30, 2011	Mar. 31, 2011
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	$ 386,186	$ 469,277
Total cash, cash equivalents and investments, gross unrealized gains	109	51
Total cash, cash equivalents and investments, gross unrealized losses	(28)	(40)
Total cash, cash equivalents and investments, fair value	386,267	469,288
Available for Sale Securities, Debt Maturities [Abstract]
Due in 1 year or less (amortized cost)	208,541	293,121
Due in 1 to 3 years (amortized cost)	56,419	39,352
Due in 1 year or less (fair value)	208,579	293,152
Due in 1 to 3 years (fair value)	56,462	39,332
Total amortized cost	264,960	332,473
Total fair value	265,041	332,484
Cash and cash equivalents [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	202,747	284,377
Total cash, cash equivalents and investments, gross unrealized gains	0	1
Total cash, cash equivalents and investments, gross unrealized losses	0	(3)
Total cash, cash equivalents and investments, fair value	202,747	284,375
Short-term Investments [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	127,020	145,548
Total cash, cash equivalents and investments, gross unrealized gains	46	35
Total cash, cash equivalents and investments, gross unrealized losses	(8)	(2)
Total cash, cash equivalents and investments, fair value	127,058	145,581
Long-term investments [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	56,419	39,352
Total cash, cash equivalents and investments, gross unrealized gains	63	15
Total cash, cash equivalents and investments, gross unrealized losses	(20)	(35)
Total cash, cash equivalents and investments, fair value	56,462	39,332
Cash [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash	121,226	136,804
Cash Equivalents [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	81,521	147,573
Total cash, cash equivalents and investments, gross unrealized gains	0	1
Total cash, cash equivalents and investments, gross unrealized losses	0	(3)
Total cash, cash equivalents and investments, fair value	81,521	147,571
U.S. Treasury Bills and Government Agency Securities [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	61,770	98,845
Total cash, cash equivalents and investments, gross unrealized gains	27	17
Total cash, cash equivalents and investments, gross unrealized losses	(4)	(1)
Total cash, cash equivalents and investments, fair value	61,793	98,861
U.S. Treasury Bills and Government Agency Securities [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	13,533	17,387
Total cash, cash equivalents and investments, gross unrealized gains	4	4
Total cash, cash equivalents and investments, gross unrealized losses	(2)	0
Total cash, cash equivalents and investments, fair value	13,535	17,391
Commercial Paper [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	45,768	30,071
Total cash, cash equivalents and investments, gross unrealized gains	10	5
Total cash, cash equivalents and investments, gross unrealized losses	0	(1)
Total cash, cash equivalents and investments, fair value	45,778	30,075
Corporate Bonds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	16,969	11,212
Total cash, cash equivalents and investments, gross unrealized gains	6	4
Total cash, cash equivalents and investments, gross unrealized losses	(4)	0
Total cash, cash equivalents and investments, fair value	16,971	11,216
Corporate Bonds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	38,005	19,086
Total cash, cash equivalents and investments, gross unrealized gains	56	8
Total cash, cash equivalents and investments, gross unrealized losses	(17)	(35)
Total cash, cash equivalents and investments, fair value	38,044	19,059
Certificates of Deposit [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	2,513	5,420
Total cash, cash equivalents and investments, gross unrealized gains	3	9
Total cash, cash equivalents and investments, gross unrealized losses	0	0
Total cash, cash equivalents and investments, fair value	2,516	5,429
Certificates of Deposit [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	4,881	2,879
Total cash, cash equivalents and investments, gross unrealized gains	3	3
Total cash, cash equivalents and investments, gross unrealized losses	(1)	0
Total cash, cash equivalents and investments, fair value	$ 4,883	$ 2,882