Unobservable Input Reconciliation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Mar. 31, 2012	Mar. 31, 2011
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	$ 12,475	$ 37,237
Included in earnings	271	138
Included in other comprehensive income (loss)	0	0
Purchases, sales, issuances, and settlements, net	(2,500)	(24,900)
Transfer into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, measurement with unobservable inputs reconciliation, ending	10,246	12,475
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		1,814
Included in earnings		(1,814)
Included in other comprehensive income (loss)		0
Purchases, sales, issuances, and settlements, net		0
Transfer into Level 3		0
Transfers out of Level 3		0
Fair value, measurement with unobservable inputs reconciliation, ending		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	0
Included in earnings	0	0
Included in other comprehensive income (loss)	0	0
Purchases, sales, issuances, and settlements, net	1,125	3,500
Transfer into Level 3	0	0
Transfers out of Level 3	0	0
Fair value, measurement with unobservable inputs reconciliation, ending	4,625	3,500
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 earnings	271	(1,676)
Included in other comprehensive income (loss)
Purchases, sales, issuances, and settlements, net
Transfer into Level 3
Transfers out of Level 3
Fair value, measurement with unobservable inputs reconciliation, ending

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in other comprehensive income (a separate component of shareholders' equity).

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents purchases, sales, issuances, and settlements (net) which have taken place during the period in relation to assets measured at fair value on a recurring basis using unobservable inputs (Level 3).

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchasesSalesIssuancesSettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Transfers into assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Transfers out of assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant