Certain Financial Statement Information - Short-Term Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Mar. 31, 2015		Sep. 30, 2014	[2]	Mar. 31, 2014	[2]
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	$ 75,394	$ 73,403
Available-for-sale Securities, Gross Unrealized Gains	124	2,020
Available-for-sale Securities, Gross Unrealized Losses	(18)	(65)
Available-for-sale Securities, Estimated Fair Value	75,500	75,358
Cash and cash equivalents	21,075	36,495	[1]	$ 53,946		$ 71,539
Short-term investments available-for-sale	54,425	38,863	[1]
Cash, Cash equivalents and Short-term investments, Estimated Fair Value	75,500	75,358
Cash
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash and Cash equivalents, Estimated Fair Value	16,224	33,936
Cash equivalents
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Cash and Cash equivalents, Estimated Fair Value	4,851	2,559
U.S Treasury securities and agency bonds
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	23,813	1,230
Available-for-sale Securities, Gross Unrealized Gains	40	0
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale Securities, Estimated Fair Value	23,853	1,230
Corporate bonds
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	24,515	10,772
Available-for-sale Securities, Gross Unrealized Gains	69	28
Available-for-sale Securities, Gross Unrealized Losses	(17)	(6)
Available-for-sale Securities, Estimated Fair Value	24,567	10,794
Asset-backed securities
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	4,633	0
Available-for-sale Securities, Gross Unrealized Gains	2	15
Available-for-sale Securities, Gross Unrealized Losses	(1)	0
Available-for-sale Securities, Estimated Fair Value	4,634	15
Municipal bonds
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	1,353	0
Available-for-sale Securities, Gross Unrealized Gains	2	0
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale Securities, Estimated Fair Value	1,355	0
Mutual Funds
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	0	24,895
Available-for-sale Securities, Gross Unrealized Gains	0	1,955
Available-for-sale Securities, Gross Unrealized Losses	0	(59)
Available-for-sale Securities, Estimated Fair Value	0	26,791
Preferred stock
Schedule of cash, cash equivalents and available-for-sale investments by type of instruments
Available-for-sale Securities, Amortized Cost	5	11
Available-for-sale Securities, Gross Unrealized Gains	11	22
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale Securities, Estimated Fair Value	$ 16	$ 33

[1] The Condensed Consolidated Balance Sheet as of March 31, 2015 has been derived from the audited Consolidated Financial Statements at that date but does not include all disclosures required by generally accepted accounting principles for complete financial statements.

[2] The Statement of Cash Flows for the six months ended September 30, 2014 reflects an immaterial revision to correct outstanding payables related to purchases of property and equipment previously included in net cash used for investing activities to net cash used for operating activities. As a result, net cash used for operating activities increased by $0.3 million and net cash used for investing activities decreased by the corresponding amount.