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Summary of Minimum And Maximum Rate of Return of Plan Assets (Detail) (Supplemental Executive Retirement Plan)	12 Months Ended
	Mar. 31, 2015
Minimum | Equity Securities
Schedule of Pension and Other Postretirement Benefits Expected Benefit Payments [Line Items]
Expected Rate of Return on Plan Assets	5.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquitySecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Minimum | Debt Securities
Schedule of Pension and Other Postretirement Benefits Expected Benefit Payments [Line Items]
Expected Rate of Return on Plan Assets	1.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_DebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Minimum | Cash and Cash Equivalents
Schedule of Pension and Other Postretirement Benefits Expected Benefit Payments [Line Items]
Expected Rate of Return on Plan Assets	0.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Maximum | Equity Securities
Schedule of Pension and Other Postretirement Benefits Expected Benefit Payments [Line Items]
Expected Rate of Return on Plan Assets	7.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_EquitySecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Maximum | Debt Securities
Schedule of Pension and Other Postretirement Benefits Expected Benefit Payments [Line Items]
Expected Rate of Return on Plan Assets	3.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_DebtSecuritiesMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Maximum | Cash and Cash Equivalents
Schedule of Pension and Other Postretirement Benefits Expected Benefit Payments [Line Items]
Expected Rate of Return on Plan Assets	1.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_CashAndCashEquivalentsMember / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember / us-gaap_RangeAxis = us-gaap_MaximumMember

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- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Expected Long-Term Rate of Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512013



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (k)(3)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920

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