Certain Financial Statement Information (Details 9) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Mar. 31, 2012		Dec. 31, 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	$ 78,200		$ 108,115
Available-for-sale investments, Gross Unrealized Gains	7,288		7,470
Available-for-sale investments, Gross Unrealized Losses	1,244		1,739
Cash, Cash equivalents and Short-term investments, Estimated Fair Value	84,244		113,846
Cash and cash equivalents	15,683		28,065		50,231	84,402
Short-term investments available-for-sale	68,561		85,781
Cash [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash and Cash equivalents, Estimated Fair Value	8,683		15,057
Cash, Cash equivalents and Short-term investments, Amortized Cost	8,683		15,057
Available-for-sale investments, Gross Unrealized Gains	0		0
Available-for-sale investments, Gross Unrealized Losses	0		0
Cash equivalents [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash and Cash equivalents, Estimated Fair Value	7,000		13,008
Cash, Cash equivalents and Short-term investments, Amortized Cost	7,000		13,008
Available-for-sale investments, Gross Unrealized Gains	0		0
Available-for-sale investments, Gross Unrealized Losses	0		0
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	12,141		16,771
Available-for-sale investments, Gross Unrealized Gains	15		11
Available-for-sale investments, Gross Unrealized Losses	2		19
Cash, Cash equivalents and Short-term investments, Estimated Fair Value	12,154		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	18,365		23,361
Available-for-sale investments, Gross Unrealized Gains	78		56
Available-for-sale investments, Gross Unrealized Losses	8		10
Cash, Cash equivalents and Short-term investments, Estimated Fair Value	18,435		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	4,076	[1]	7,308	[1]
Available-for-sale investments, Gross Unrealized Gains	349	[1]	364	[1]
Available-for-sale investments, Gross Unrealized Losses	9	[1]	61	[1]
Cash, Cash equivalents and Short-term investments, Estimated Fair Value	4,416	[1]	7,611	[1]
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	23,057		26,401
Available-for-sale investments, Gross Unrealized Gains	4,959		5,161
Available-for-sale investments, Gross Unrealized Losses	1,225		1,649
Cash, Cash equivalents and Short-term investments, Estimated Fair Value	26,791		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	1,887		1,878
Available-for-sale investments, Gross Unrealized Losses	0		0
Cash, Cash equivalents and Short-term investments, Estimated Fair Value	$ 6,765		$ 8,087

[1] At December 31, 2012 and March 31, 2012, approximately $1.7 million and $4.6 million of the estimated fair value presented were mortgage-backed securities, respectively.