Changes in level 3 assets measured at fair value (Detail) (USD $) In Thousands, unless otherwise specified
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12 Months Ended |
Dec. 31, 2014
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Dec. 31, 2013
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Assets, Fair Value Disclosure [Abstract] |
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Fair value of plan assets at end of year |
$ 697,240us-gaap_DefinedBenefitPlanFairValueOfPlanAssets |
$ 705,482us-gaap_DefinedBenefitPlanFairValueOfPlanAssets |
Fair Value, Inputs, Level 3 [Member] |
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Assets, Fair Value Disclosure [Abstract] |
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Fair value of plan assets at beginning of year |
2,562us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
2,848us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Defined Benefit Plan, Actual Return on Plan Assets Still Held |
(459)us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
(286)us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Defined Benefit Plan, Purchases, Sales, and Settlements |
0us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
0us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Fair value of plan assets at end of year |
2,103us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
2,562us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
Private Equity Investment [Member] |
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Assets, Fair Value Disclosure [Abstract] |
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Fair value of plan assets at end of year |
546us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_PrivateEquityFundsMember |
922us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_PrivateEquityFundsMember |
Private Equity Investment [Member] | Fair Value, Inputs, Level 3 [Member] |
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Assets, Fair Value Disclosure [Abstract] |
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Fair value of plan assets at end of year |
$ 546us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_PrivateEquityFundsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |
$ 922us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis = us-gaap_PrivateEquityFundsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member |