Certain Financial Statement Information - Short-Term Investments Gross Unrealized Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Mar. 31, 2016
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	$ 7,728	$ 22,391
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	(17)	(35)
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	7,728	22,391
Total Gross Unrealized Losses	(17)	(35)
U.S. Treasury and agency securities
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	2,149	9,396
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	(2)	(3)
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	2,149	9,396
Total Gross Unrealized Losses	(2)	(3)
Corporate bonds
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	1,906	4,601
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	(2)	(5)
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	1,906	4,601
Total Gross Unrealized Losses	(2)	(5)
Asset-backed and mortgage-backed securities
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	3,673	8,394
Less than 12 Months of Unrealized Losses, Gross Unrealized Losses	(13)	(27)
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	3,673	8,394
Total Gross Unrealized Losses	$ (13)	$ (27)