Certain Financial Statement Information - Short-Term Investments Gross Unrealized Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Mar. 31, 2015
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	$ 48,194	$ 15,470
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	(177)	(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	48,194	15,945
Total Gross Unrealized Losses	(177)	(65)
U.S. Treasury securities and agency bonds
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	17,260
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	(54)
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	17,260
Total Gross Unrealized Losses	(54)
Corporate bonds
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	18,243	878
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	(63)	(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	18,243	878
Total Gross Unrealized Losses	(63)	(6)
Asset-backed and mortgage-backed securities
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	10,793
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	(50)
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	10,793
Total Gross Unrealized Losses	(50)
Municipal bonds
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	1,898
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	(10)
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	1,898
Total Gross Unrealized Losses	$ (10)
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)