CASH, CASH EQUIVALENTS, AND INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Sep. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Mar. 31, 2012
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and Cash Equivalents, Fair Value	$ 245,980	$ 228,776	$ 207,929	$ 209,335
Cash, Cash Equivalents Before Unrealized Gains And Losses, and Amortized Cost Basis of Available-For-Sale Securities	438,473	425,501
Cash Equivalents and Available-For-Sale Securities, Gross Unrealized Gains	169	126
Cash Equivalents and Available-For-Sale Securities, Gross Unrealized Losses	(44)	(9)
Cash and Fair Value of Cash Equivalents and Available-For-Sale Securities	438,598	425,618
Available for Sale Securities, Debt Maturities [Abstract]
Due in 1 year or less (amortized cost)	122,702	226,423
Due in 1 to 3 years (amortized cost)	79,399	80,197
Due in 1 year or less (fair value)	122,751	226,476
Due in 1 to 3 years (fair value)	79,475	80,261
Total amortized cost	202,101	306,620
Total fair value	202,226	306,737
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	15,473	55,317
Available-for-sale securities, gross unrealized gains	18	42
Available-for-sale securities, gross unrealized losses	(4)	(1)
Available-for-sale securities, fair value	15,487	55,358
Corporate Bonds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	63,926	23,878
Available-for-sale securities, gross unrealized gains	85	23
Available-for-sale securities, gross unrealized losses	(23)	(3)
Available-for-sale securities, fair value	63,988	23,898
Certificates of Deposit [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	0	1,002
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	1,005
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	56,964	66,092
Available-for-sale securities, gross unrealized gains	33	18
Available-for-sale securities, gross unrealized losses	(15)	(3)
Available-for-sale securities, fair value	56,982	66,107
Commercial Paper [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	30,835	15,670
Available-for-sale securities, gross unrealized gains	12	9
Available-for-sale securities, gross unrealized losses	(1)	0
Available-for-sale securities, fair value	30,846	15,679
Corporate Bonds [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	24,294	34,766
Available-for-sale securities, gross unrealized gains	19	31
Available-for-sale securities, gross unrealized losses	(1)	(2)
Available-for-sale securities, fair value	24,312	34,795
Certificates of Deposit [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	1,002
Available-for-sale securities, gross unrealized gains	1
Available-for-sale securities, gross unrealized losses	0
Available-for-sale securities, fair value	1,003
Cash [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash	236,372	118,881
Cash Equivalents [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash Equivalents Before Unrealized Gains And Losses	9,607	109,895
Cash Equivalents, Gross Unrealized Gains	1	0
Cash Equivalents, Gross Unrealized Losses	0	0
Cash equivalents, fair value	9,608	109,895
Cash and cash equivalents [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Cash and Cash Equivalents Before Unrealized Gains And Losses	245,979	228,776
Cash Equivalents, Gross Unrealized Gains	1	0
Cash Equivalents, Gross Unrealized Losses	0	0
Cash and Cash Equivalents, Fair Value	245,980	228,776
Short-term Investments [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	113,095	116,528
Available-for-sale securities, gross unrealized gains	65	58
Available-for-sale securities, gross unrealized losses	(17)	(5)
Available-for-sale securities, fair value	113,143	116,581
Long-term investments [Member]
Schedule of Cash, Cash Equivalents and Investments [Line Items]
Available-for-sale securities, amortized cost basis	79,399	80,197
Available-for-sale securities, gross unrealized gains	103	68
Available-for-sale securities, gross unrealized losses	(27)	(4)
Available-for-sale securities, fair value	$ 79,475	$ 80,261