Certain Financial Statement Information (Details 9) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012		Sep. 30, 2011	Mar. 31, 2011
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash, cash equivalents and short- term investments, Amortized Cost	$ 82,535	$ 108,115
Available-for-sale investments, Gross Unrealized Gains	8,282	7,470
Available-for-sale investments, Gross Unrealized Losses	1,130	1,739
Cash cash equivalents and short term investments, Estimated Fair Value	89,687	113,846
Cash and cash equivalents	11,992	28,065	[1]	51,783	84,402
Short-term investments available-for-sale	77,695	85,781	[1]
Cash [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash and cash Equivalents, Estimated Fair Value	9,902	15,057
Cash, cash equivalents and short- term investments, Amortized Cost	9,902	15,057
Available-for-sale investments, Gross Unrealized Gains
Available-for-sale investments, Gross Unrealized Losses
Cash equivalents [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash and cash Equivalents, Estimated Fair Value	2,090	13,008
Cash, cash equivalents and short- term investments, Amortized Cost	2,090	13,008
Available-for-sale investments, Gross Unrealized Gains
Available-for-sale investments, Gross Unrealized Losses
U.S Treasury securities and agency bonds [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash, cash equivalents and short- term investments, Amortized Cost	17,533	16,771
Available-for-sale investments, Gross Unrealized Gains	23	11
Available-for-sale investments, Gross Unrealized Losses	1	19
Cash cash equivalents and short term investments, Estimated Fair Value	17,555	16,763
Corporate bonds [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash, cash equivalents and short- term investments, Amortized Cost	20,485	23,361
Available-for-sale investments, Gross Unrealized Gains	95	56
Available-for-sale investments, Gross Unrealized Losses	6	10
Cash cash equivalents and short term investments, Estimated Fair Value	20,574	23,407
Mortgage-backed and asset-backed securities [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash, cash equivalents and short- term investments, Amortized Cost	3,942	7,308
Available-for-sale investments, Gross Unrealized Gains	398	364
Available-for-sale investments, Gross Unrealized Losses	26	61
Cash cash equivalents and short term investments, Estimated Fair Value	4,314	7,611
Closed-end bond funds [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash, cash equivalents and short- term investments, Amortized Cost	23,705	26,401
Available-for-sale investments, Gross Unrealized Gains	5,760	5,161
Available-for-sale investments, Gross Unrealized Losses	1,097	1,649
Cash cash equivalents and short term investments, Estimated Fair Value	28,368	29,913
Preferred stock [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash, cash equivalents and short- term investments, Amortized Cost	4,878	6,209
Available-for-sale investments, Gross Unrealized Gains	2,006	1,878
Available-for-sale investments, Gross Unrealized Losses
Cash cash equivalents and short term investments, Estimated Fair Value	$ 6,884	$ 8,087

[1] Note: Amounts have been derived from the March 31, 2012 audited consolidated financial statements.