Unobservable Input Reconciliation Assets (Details) (USD $)	3 Months Ended	12 Months Ended
	Jun. 30, 2012	Mar. 31, 2012
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	$ 10,246,000	$ 12,475,000
Included in earnings	0	271,000
Included in other comprehensive income (loss)	0	0
Purchases, sales, issuances, and settlements, net	0	(2,500,000)
Transfer into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, measurement with unobservable inputs reconciliation, ending	10,246,000	10,246,000
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	4,625,000	3,500,000
Included in earnings	0	0
Included in other comprehensive income (loss)	0	0
Purchases, sales, issuances, and settlements, net	0	1,125,000
Transfer into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, measurement with unobservable inputs reconciliation, ending	4,625,000	4,625,000
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	0	0
Included in earnings	0	271,000
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