CASH, CASH EQUIVALENTS AND INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2010
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 228,776	$ 209,335	$ 277,373	$ 349,961
Cash, Cash Equivalents Before Unrealized Gains And Losses, and Amortized Cost Basis of Available-For-Sale Securities	425,501	389,777
Cash Equivalents and Available-For-Sale Securities, Gross Unrealized Gains	126	141
Cash Equivalents and Available-For-Sale Securities, Gross Unrealized Losses	(9)	(59)
Cash and Fair Value of Cash Equivalents and Available-For-Sale Securities	425,618	389,859
Available for Sale Securities, Debt Maturities [Abstract]
Due in 1 year or less (amortized cost)	226,423	187,118
Due in 1 to 3 years (amortized cost)	80,197	55,321
Due in 1 year or less (fair value)	226,476	187,174
Due in 1 to 3 years (fair value)	80,261	55,347
Total amortized cost	306,620	242,439
Total fair value	306,737	242,521
U.S. Treasury Bills and Government Agency Securities
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale Securities, amortized cost basis	55,317	29,814
Available-for-sale Securities, gross unrealized gains	42	24
Available-for-sale Securities, gross unrealized losses	(1)	(1)
Available-for-sale Securities, fair value	55,358	29,837
Corporate Bonds
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale Securities, amortized cost basis	23,878	25,507
Available-for-sale Securities, gross unrealized gains	23	29
Available-for-sale Securities, gross unrealized losses	(3)	(26)
Available-for-sale Securities, fair value	23,898	25,510
Certificates of Deposit
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	3	0
Available-for-sale Securities, gross unrealized losses	0	0
Available-for-sale Securities, fair value	1,005	0
U.S. Treasury Bills and Government Agency Securities
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale Securities, amortized cost basis	66,092	61,898
Available-for-sale Securities, gross unrealized gains	18	22
Available-for-sale Securities, gross unrealized losses	(3)	(24)
Available-for-sale Securities, fair value	66,107	61,896
Commercial Paper
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale Securities, amortized cost basis	15,670	20,041
Available-for-sale Securities, gross unrealized gains	9	1
Available-for-sale Securities, gross unrealized losses	0	(3)
Available-for-sale Securities, fair value	15,679	20,039
Corporate Bonds
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale Securities, amortized cost basis	34,766	38,300
Available-for-sale Securities, gross unrealized gains	31	60
Available-for-sale Securities, gross unrealized losses	(2)	(4)
Available-for-sale Securities, fair value	34,795	38,356
Certificates of Deposit
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale Securities, amortized cost basis	0	4,883
Available-for-sale Securities, gross unrealized gains	0	3
Available-for-sale Securities, gross unrealized losses	0	0
Available-for-sale Securities, fair value	0	4,886
Cash
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash	118,881	147,338
Cash Equivalents
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash Equivalents Before Unrealized Gains And Losses	109,895	61,996
Cash Equivalents, Gross Unrealized Gains	0	2
Cash Equivalents, Gross Unrealized Losses	0	(1)
Cash Equivalents, at Carrying Value	109,895	61,997
Cash and cash equivalents | Cash and cash equivalents
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and Cash Equivalents Before Unrealized Gains And Losses	228,776	209,334
Cash Equivalents, Gross Unrealized Gains	0	2
Cash Equivalents, Gross Unrealized Losses	0	(1)
Cash and Cash Equivalents, at Carrying Value	228,776	209,335
Short-term Investments
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale Securities, amortized cost basis	116,528	125,122
Available-for-sale Securities, gross unrealized gains	58	86
Available-for-sale Securities, gross unrealized losses	(5)	(31)
Available-for-sale Securities, fair value	116,581	125,177
Long-term Investments
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale Securities, amortized cost basis	80,197	55,321
Available-for-sale Securities, gross unrealized gains	68	53
Available-for-sale Securities, gross unrealized losses	(4)	(27)
Available-for-sale Securities, fair value	$ 80,261	$ 55,347