Unobservable Input Reconciliation (Details) (USD $)	3 Months Ended		6 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Reconciliation for all assets measured at fair value on a recurring basis, excluding accrued interest components, using significant unobservable inputs [Rollforward]
Included in earnings	$ (395,000)	$ (388,000)	$ (782,000)	$ (840,000)
Auction rate securities [Member]
Reconciliation for all assets measured at fair value on a recurring basis, excluding accrued interest components, using significant unobservable inputs [Rollforward]
Fair value, measurement with unobservable inputs reconciliation, beginning	12,088,000	20,396,000	12,475,000	37,237,000
Included in earnings	(395,000)	65,000	(782,000)	974,000
Included in other comprehensive income (loss)	0	0	0	0
Purchases, sales, issuances, and settlements, net	0	(7,150,000)	0	(24,900,000)
Transfer into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Fair value, measurement with unobservable inputs reconciliation, ending	11,693,000	13,311,000	11,693,000	13,311,000
Put Option on Auction Rate Securities [Member]
Reconciliation for all assets measured at fair value on a recurring basis, excluding accrued interest components, using significant unobservable inputs [Rollforward]
Fair value, measurement with unobservable inputs reconciliation, beginning		453,000		1,814,000
Included in earnings		(453,000)		(1,814,000)
Included in other comprehensive income (loss)		0		0
Purchases, sales, issuances, and settlements, net		0		0
Transfer into Level 3		0		0
Transfers out of Level 3		0		0
Fair value, measurement with unobservable inputs reconciliation, ending		0		0
Corporate Debt [Member]
Reconciliation for all assets measured at fair value on a recurring basis, excluding accrued interest components, using significant unobservable inputs [Rollforward]
Fair value, measurement with unobservable inputs reconciliation, beginning	3,500,000	3,500,000	3,500,000	0
Included in earnings	0	0	0	0
Included in other comprehensive income (loss)	0	0	0	0
Purchases, sales, issuances, and settlements, net	787,000	0	787,000	3,500,000
Transfer into Level 3	338,000	0	338,000	0
Transfers out of Level 3	0	0	0	0
Fair value, measurement with unobservable inputs reconciliation, ending	4,625,000	3,500,000	4,625,000	3,500,000
Total Gains (Losses) [Member]
Reconciliation for all assets measured at fair value on a recurring basis, excluding accrued interest components, using significant unobservable inputs [Rollforward]
Fair value, measurement with unobservable inputs reconciliation, beginning
Included in other comprehensive income (loss)
Purchases, sales, issuances, and settlements, net
Transfer into Level 3
Transfers out of Level 3