Certain Financial Statement Information - Short-Term Investments Gross Unrealized Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Mar. 31, 2015
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	$ 9,600	$ 15,470
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	(18)	(23)
12 Months or More of Unrealized Losses, Estimated Fair Value	0	475
12 Months or More of Unrealized Losses, Gross Unrealized Losses	0	(42)
Total, Estimated Fair Value	9,600	15,945
Total Gross Unrealized Losses	(18)	(65)
U.S. Treasury securities and agency bonds
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	1,579
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	0
12 Months or More of Unrealized Losses, Estimated Fair Value	0
12 Months or More of Unrealized Losses, Gross Unrealized Losses	0
Total, Estimated Fair Value	1,579
Total Gross Unrealized Losses	0
Corporate bonds
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	6,617	878
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	(17)	(6)
12 Months or More of Unrealized Losses, Estimated Fair Value	0	0
12 Months or More of Unrealized Losses, Gross Unrealized Losses	0	0
Total, Estimated Fair Value	6,617	878
Total Gross Unrealized Losses	(17)	(6)
Asset-backed securities
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	1,404
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	(1)
12 Months or More of Unrealized Losses, Estimated Fair Value	0
12 Months or More of Unrealized Losses, Gross Unrealized Losses	0
Total, Estimated Fair Value	1,404
Total Gross Unrealized Losses	$ (1)
Mutual Funds
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value		14,592
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses		(17)
12 Months or More of Unrealized Losses, Estimated Fair Value		475
12 Months or More of Unrealized Losses, Gross Unrealized Losses		(42)
Total, Estimated Fair Value		15,067
Total Gross Unrealized Losses		$ (59)