Certain Financial Statement Information (Details 12) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	$ 4,077	$ 15,295
Less Than 12 Months of Unrealized Losses, Gross Unrealized Losses	12	49
12 Months or More of Unrealized Losses, Estimated Fair Value	7,660	6,981
12 Months or More of Unrealized Losses, Gross Unrealized Losses	1,118	1,690
Total, Estimated Fair Value	11,737	22,276
Total, Gross Unrealized Losses	1,130	1,739
U.S Treasury securities and agency bonds [Member]
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	2,456	8,938
Less Than 12 Months of Unrealized Losses, Gross Unrealized Losses		19
12 Months or More of Unrealized Losses, Estimated Fair Value
12 Months or More of Unrealized Losses, Gross Unrealized Losses
Total, Estimated Fair Value	2,456	8,938
Total, Gross Unrealized Losses		19
Corporate bonds [Member]
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	898	5,463
Less Than 12 Months of Unrealized Losses, Gross Unrealized Losses	4	10
12 Months or More of Unrealized Losses, Estimated Fair Value	248
12 Months or More of Unrealized Losses, Gross Unrealized Losses	2
Total, Estimated Fair Value	1,146	5,463
Total, Gross Unrealized Losses	6	10
Mortgage-backed and asset-backed securities [Member]
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value	723	894
Less Than 12 Months of Unrealized Losses, Gross Unrealized Losses	8	20
12 Months or More of Unrealized Losses, Estimated Fair Value	232	353
12 Months or More of Unrealized Losses, Gross Unrealized Losses	18	42
Total, Estimated Fair Value	955	1,247
Total, Gross Unrealized Losses	26	62
Closed-end bond funds [Member]
Schedule of Gross Unrealized Losses
Less Than 12 Months of Unrealized Losses, Estimated Fair Value
Less Than 12 Months of Unrealized Losses, Gross Unrealized Losses
12 Months or More of Unrealized Losses, Estimated Fair Value	7,180	6,628
12 Months or More of Unrealized Losses, Gross Unrealized Losses	1,098	1,648
Total, Estimated Fair Value	7,180	6,628
Total, Gross Unrealized Losses	$ 1,098	$ 1,648