CASH, CASH EQUIVALENTS AND INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010	Mar. 31, 2010
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 178,063	$ 277,373	$ 257,887	$ 349,961
Cash, Cash Equivalents Before Unrealized Gains And Losses, and Amortized Cost Basis of Available-For-Sale Securities	359,625	469,277
Cash Equivalents and Available-For-Sale Securities, Gross Unrealized Gains	93	51
Cash Equivalents and Available-For-Sale Securities, Gross Unrealized Losses	(235)	(40)
Cash and Fair Value of Cash Equivalents and Available-For-Sale Securities	359,483	469,288
Available for Sale Securities, Debt Maturities [Abstract]
Due in 1 year or less (amortized cost)	136,453	293,121
Due in 1 to 3 years (amortized cost)	62,103	39,352
Due in 1 year or less (fair value)	136,453	293,152
Due in 1 to 3 years (fair value)	61,961	39,332
Total amortized cost	198,556	332,473
Total fair value	198,414	332,484
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	39,176	17,387
Total cash, cash equivalents and investments, gross unrealized gains	26	4
Total cash, cash equivalents and investments, gross unrealized losses	(10)	0
Total cash, cash equivalents and investments, fair value	39,192	17,391
Corporate Bonds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	20,924	19,086
Total cash, cash equivalents and investments, gross unrealized gains	13	8
Total cash, cash equivalents and investments, gross unrealized losses	(170)	(35)
Total cash, cash equivalents and investments, fair value	20,767	19,059
Certificates of Deposit [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	2,003	2,879
Total cash, cash equivalents and investments, gross unrealized gains	0	3
Total cash, cash equivalents and investments, gross unrealized losses	(1)	0
Total cash, cash equivalents and investments, fair value	2,002	2,882
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	76,530	105,849
Total cash, cash equivalents and investments, gross unrealized gains	22	17
Total cash, cash equivalents and investments, gross unrealized losses	(10)	(3)
Total cash, cash equivalents and investments, fair value	76,542	105,863
Commercial Paper [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	15,679	30,071
Total cash, cash equivalents and investments, gross unrealized gains	4	5
Total cash, cash equivalents and investments, gross unrealized losses	(3)	(1)
Total cash, cash equivalents and investments, fair value	15,680	30,075
Corporate Bonds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	24,372	11,212
Total cash, cash equivalents and investments, gross unrealized gains	22	4
Total cash, cash equivalents and investments, gross unrealized losses	(41)	0
Total cash, cash equivalents and investments, fair value	24,353	11,216
Certificates of Deposit [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	2,880	5,420
Total cash, cash equivalents and investments, gross unrealized gains	4	9
Total cash, cash equivalents and investments, gross unrealized losses	0	0
Total cash, cash equivalents and investments, fair value	2,884	5,429
Cash [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash	161,069	136,804
Cash Equivalents [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash Equivalents, Gross Unrealized Gains	2	1
Cash Equivalents, Gross Unrealized Losses	0	(1)
Cash Equivalents, at Carrying Value	16,994	140,569
Cash Equivalents Before Unrealized Gains And Losses	16,992	140,569
Cash and cash equivalents [Member] | Cash and cash equivalents [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and Cash Equivalents Before Unrealized Gains And Losses	178,061	277,373
Cash Equivalents, Gross Unrealized Gains	2	1
Cash Equivalents, Gross Unrealized Losses	0	(1)
Cash and Cash Equivalents, at Carrying Value	178,063	277,373
Short-term Investments [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	119,461	152,552
Total cash, cash equivalents and investments, gross unrealized gains	52	35
Total cash, cash equivalents and investments, gross unrealized losses	(54)	(4)
Total cash, cash equivalents and investments, fair value	119,459	152,583
Long-term investments [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Total cash, cash equivalents and investments, amortized cost basis	62,103	39,352
Total cash, cash equivalents and investments, gross unrealized gains	39	15
Total cash, cash equivalents and investments, gross unrealized losses	(181)	(35)
Total cash, cash equivalents and investments, fair value	$ 61,961	$ 39,332