CASH, CASH EQUIVALENTS AND INVESTMENTS (Details) (USD $) In Thousands	Sep. 30, 2011	Mar. 31, 2011	Sep. 30, 2010	Mar. 31, 2010
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	$ 349,206	$ 469,277
Total cash, cash equivalents and investments, gross unrealized gains	73	51
Total cash, cash equivalents and investments, gross unrealized losses	(290)	(40)
Cash and Cash Equivalents, at Carrying Value	185,377	284,375	294,429	349,961
Total cash, cash equivalents and investments, fair value	348,989	469,288
Available for Sale Securities, Debt Maturities [Abstract]
Due in 1 year or less (amortized cost)	121,063	293,121
Due in 1 to 3 years (amortized cost)	59,268	39,352
Due in 1 year or less (fair value)	121,084	293,152
Due in 1 to 3 years (fair value)	59,030	39,332
Total amortized cost	180,331	332,473
Total fair value	180,114	332,484
Cash and cash equivalents [Member] | Cash and cash equivalents [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	185,375	284,377
Total cash, cash equivalents and investments, gross unrealized gains	2	1
Total cash, cash equivalents and investments, gross unrealized losses	0	(3)
Total cash, cash equivalents and investments, fair value	185,377	284,375
Cash [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash	168,875	136,804
Cash Equivalents [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	16,500	147,573
Total cash, cash equivalents and investments, gross unrealized gains	2	1
Total cash, cash equivalents and investments, gross unrealized losses	0	(3)
Total cash, cash equivalents and investments, fair value	16,502	147,571
Short-term Investments [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	104,563	145,548
Total cash, cash equivalents and investments, gross unrealized gains	35	35
Total cash, cash equivalents and investments, gross unrealized losses	(16)	(2)
Total cash, cash equivalents and investments, fair value	104,582	145,581
Long-term investments [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	59,268	39,352
Total cash, cash equivalents and investments, gross unrealized gains	36	15
Total cash, cash equivalents and investments, gross unrealized losses	(274)	(35)
Total cash, cash equivalents and investments, fair value	59,030	39,332
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	61,988	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	62,011	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	21,071	17,387
Total cash, cash equivalents and investments, gross unrealized gains	8	4
Total cash, cash equivalents and investments, gross unrealized losses	(24)	0
Total cash, cash equivalents and investments, fair value	21,055	17,391
Commercial Paper [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	17,988	30,071
Total cash, cash equivalents and investments, gross unrealized gains	1	5
Total cash, cash equivalents and investments, gross unrealized losses	0	(1)
Total cash, cash equivalents and investments, fair value	17,989	30,075
Corporate Bonds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	22,070	11,212
Total cash, cash equivalents and investments, gross unrealized gains	6	4
Total cash, cash equivalents and investments, gross unrealized losses	(12)	0
Total cash, cash equivalents and investments, fair value	22,064	11,216
Corporate Bonds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	33,316	19,086
Total cash, cash equivalents and investments, gross unrealized gains	17	8
Total cash, cash equivalents and investments, gross unrealized losses	(249)	(35)
Total cash, cash equivalents and investments, fair value	33,084	19,059
Certificates of Deposit [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	2,517	5,420
Total cash, cash equivalents and investments, gross unrealized gains	1	9
Total cash, cash equivalents and investments, gross unrealized losses	0	0
Total cash, cash equivalents and investments, fair value	2,518	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	11	3
Total cash, cash equivalents and investments, gross unrealized losses	(1)	0
Total cash, cash equivalents and investments, fair value	$ 4,891	$ 2,882