Certain Financial Statement Information Short-Term Investments (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Sep. 30, 2014		Mar. 31, 2014		Sep. 30, 2013	Mar. 31, 2013
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	$ 86,102		$ 103,548
Available-for-sale Securities, Gross Unrealized Gain	3,551		3,455
Available-for-sale Securities, Gross Unrealized Loss	135		420
Available-for-sale Securities, Estimated Fair Value	89,518		106,583
Cash and cash equivalents	53,946		71,539		27,908	19,065
Short-term investments available-for-sale	35,572		35,044
Cash, Cash equivalents and Short-term investments, Estimated Fair Value	89,518		106,583
Cash [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash and Cash equivalents, Estimated Fair Value	47,709		65,867
Cash equivalents [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash and Cash equivalents, Estimated Fair Value	6,237		5,672
U.S Treasury securities and agency bonds [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	2,842		2,838
Available-for-sale Securities, Gross Unrealized Gain	0		0
Available-for-sale Securities, Gross Unrealized Loss	0		0
Available-for-sale Securities, Estimated Fair Value	2,842		2,838
Corporate bonds [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	10,881		10,599
Available-for-sale Securities, Gross Unrealized Gain	24		30
Available-for-sale Securities, Gross Unrealized Loss	4		2
Available-for-sale Securities, Estimated Fair Value	10,901		10,627
Mortgage-backed and asset-backed securities [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	1,654		1,793
Available-for-sale Securities, Gross Unrealized Gain	309		297
Available-for-sale Securities, Gross Unrealized Loss	3		16
Available-for-sale Securities, Estimated Fair Value	1,960	[1]	2,074	[1]
Closed-end bond funds [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	14,373		14,373
Available-for-sale Securities, Gross Unrealized Gain	2,437		2,392
Available-for-sale Securities, Gross Unrealized Loss	128		402
Available-for-sale Securities, Estimated Fair Value	16,682		16,363
Preferred stock [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	2,406		2,406
Available-for-sale Securities, Gross Unrealized Gain	781		736
Available-for-sale Securities, Gross Unrealized Loss	0		0
Available-for-sale Securities, Estimated Fair Value	3,187		3,142
Mortgage-backed securities [Member]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash, Cash equivalents and Short-term investments, Estimated Fair Value	$ 1,000	[1]	$ 1,100	[1]

[1] At September 30, 2014 and March 31, 2014, approximately $1.0 million and $1.1 million of the estimated fair value presented were mortgage-backed securities, respectively.