CASH, CASH EQUIVALENTS AND INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and Cash Equivalents, Fair Value	$ 196,656	$ 209,335	$ 178,063	$ 277,373
Cash, Cash Equivalents Before Unrealized Gains And Losses, and Amortized Cost Basis of Available-For-Sale Securities	408,402	389,777
Cash Equivalents and Available-For-Sale Securities, Gross Unrealized Gains	133	141
Cash Equivalents and Available-For-Sale Securities, Gross Unrealized Losses	(15)	(59)
Cash and Fair Value of Cash Equivalents and Available-For-Sale Securities	408,520	389,859
Available for Sale Securities, Debt Maturities [Abstract]
Due in 1 year or less (amortized cost)	181,876	187,118
Due in 1 to 3 years (amortized cost)	79,561	55,321
Due in 1 year or less (fair value)	181,936	187,174
Due in 1 to 3 years (fair value)	79,619	55,347
Total amortized cost	261,437	242,439
Total fair value	261,555	242,521
U.S. Treasury Bills and Government Agency Securities [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	63,939	29,814
Available-for-sale securities, gross unrealized gains	40	24
Available-for-sale securities, gross unrealized losses	0	(1)
Available-for-sale securities, fair value	63,979	29,837
Corporate Bonds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	14,620	25,507
Available-for-sale securities, gross unrealized gains	20	29
Available-for-sale securities, gross unrealized losses	(6)	(26)
Available-for-sale securities, fair value	14,634	25,510
Certificates of Deposit [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	1,002	0
Available-for-sale securities, gross unrealized gains	4	0
Available-for-sale securities, gross unrealized losses	0	0
Available-for-sale securities, fair value	1,006	0
U.S. Treasury Bills and Government Agency Securities [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	65,530	61,898
Available-for-sale securities, gross unrealized gains	28	22
Available-for-sale securities, gross unrealized losses	0	(24)
Available-for-sale securities, fair value	65,558	61,896
Commercial Paper [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	28,384	20,041
Available-for-sale securities, gross unrealized gains	6	1
Available-for-sale securities, gross unrealized losses	0	(3)
Available-for-sale securities, fair value	28,390	20,039
Corporate Bonds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	36,270	38,300
Available-for-sale securities, gross unrealized gains	33	60
Available-for-sale securities, gross unrealized losses	(9)	(4)
Available-for-sale securities, fair value	36,294	38,356
Certificates of Deposit [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	2,002	4,883
Available-for-sale securities, gross unrealized gains	1	3
Available-for-sale securities, gross unrealized losses	0	0
Available-for-sale securities, fair value	2,003	4,886
Cash [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash	146,965	147,338
Cash Equivalents [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash Equivalents Before Unrealized Gains And Losses	49,690	61,996
Cash Equivalents, Gross Unrealized Gains	1	2
Cash Equivalents, Gross Unrealized Losses	0	(1)
Cash equivalents, fair value	49,691	61,997
Cash and cash equivalents [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and Cash Equivalents Before Unrealized Gains And Losses	196,655	209,334
Cash Equivalents, Gross Unrealized Gains	1	2
Cash Equivalents, Gross Unrealized Losses	0	(1)
Cash and Cash Equivalents, Fair Value	196,656	209,335
Short-term Investments [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	132,186	125,122
Available-for-sale securities, gross unrealized gains	68	86
Available-for-sale securities, gross unrealized losses	(9)	(31)
Available-for-sale securities, fair value	132,245	125,177
Long-term investments [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	79,561	55,321
Available-for-sale securities, gross unrealized gains	64	53
Available-for-sale securities, gross unrealized losses	(6)	(27)
Available-for-sale securities, fair value	$ 79,619	$ 55,347