INVESTMENTS (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Total investments
Amortized Cost	$ 207,361	$ 162,352
Gross Unrealized Gains	64	954
Gross Unrealized Losses, Less than One Year	(45)	(109)
Gross Unrealized Losses, Greater than One Year	(162)	(660)
Estimated Fair Value	207,218	162,537
Short-term investments
Available-for-sale securities:
Amortized Cost	123,128	100,895
Gross Unrealized Gains	64	116
Gross Unrealized Losses, Less than One Year	(2)	(19)
Estimated Fair Value	123,190	100,992
Held-to-maturity securities:
Amortized Cost		4,653
Estimated Fair Value		4,653
Total investments
Amortized Cost	124,329	106,749
Gross Unrealized Gains	64	116
Gross Unrealized Losses, Less than One Year	(2)	(19)
Estimated Fair Value	124,391	106,846
Short-term investments | Money market funds
Total investments
Amortized Cost	1,201	1,201
Estimated Fair Value	1,201	1,201
Short-term investments | Certificates of deposit
Held-to-maturity securities:
Amortized Cost		4,236
Estimated Fair Value		4,236
Short-term investments | U.S. government obligations
Held-to-maturity securities:
Amortized Cost		417
Estimated Fair Value		417
Short-term investments | U.S. government and agency debt securities
Available-for-sale securities:
Amortized Cost	102,093	62,925
Gross Unrealized Gains	29	67
Gross Unrealized Losses, Less than One Year	(1)	(17)
Estimated Fair Value	102,121	62,975
Short-term investments | International government agency debt securities
Available-for-sale securities:
Amortized Cost	10,089	25,646
Gross Unrealized Gains	8	22
Gross Unrealized Losses, Less than One Year	(1)	(2)
Estimated Fair Value	10,096	25,666
Short-term investments | Corporate debt securities
Available-for-sale securities:
Amortized Cost	10,946	12,324
Gross Unrealized Gains	27	27
Estimated Fair Value	10,973	12,351
Long-term investments
Available-for-sale securities:
Amortized Cost	81,832	54,403
Gross Unrealized Gains		838
Gross Unrealized Losses, Less than One Year	(43)	(90)
Gross Unrealized Losses, Greater than One Year	(162)	(660)
Estimated Fair Value	81,627	54,491
Held-to-maturity securities:
Amortized Cost	83,032	55,603
Gross Unrealized Gains		838
Gross Unrealized Losses, Less than One Year	(43)	(90)
Gross Unrealized Losses, Greater than One Year	(162)	(660)
Estimated Fair Value	82,827	55,691
Long-term investments | Certificates of deposit
Held-to-maturity securities:
Amortized Cost	1,200	1,200
Estimated Fair Value	1,200	1,200
Long-term investments | U.S. government and agency debt securities
Available-for-sale securities:
Amortized Cost	60,047	35,493
Gross Unrealized Losses, Less than One Year	(17)	(70)
Estimated Fair Value	60,030	35,423
Long-term investments | International government agency debt securities
Available-for-sale securities:
Amortized Cost	3,060	10,257
Gross Unrealized Losses, Less than One Year		(20)
Estimated Fair Value	3,060	10,237
Long-term investments | Corporate debt securities
Available-for-sale securities:
Amortized Cost	18,725	8,009
Gross Unrealized Losses, Less than One Year	(26)
Gross Unrealized Losses, Greater than One Year	(162)	(660)
Estimated Fair Value	18,537	7,349
Long-term investments | Strategic investments
Available-for-sale securities:
Amortized Cost		644
Gross Unrealized Gains		838
Estimated Fair Value		$ 1,482