XML 18 R54.htm IDEA: XBRL DOCUMENT v2.4.1.9
Employee Benefit Plans (Schedule of Fair Value of Pension Plan Assets) (Details) (Pension Benefit Plan [Member], USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 51,623us-gaap_DefinedBenefitPlanFairValueOfPlanAssets $ 46,443us-gaap_DefinedBenefitPlanFairValueOfPlanAssets $ 37,904us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
Mutual Funds - Small Cap Core [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 261us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= us-gaap_PensionPlansDefinedBenefitMember		  
Mutual Funds - Small Cap Value [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 876us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= us-gaap_PensionPlansDefinedBenefitMember		  
Mutual Funds - Mid Cap Core [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,013us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsMidCapCoreMember
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Mutual Funds - Mid Cap Growth [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets   1,015us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsMidCapGrowthMember
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Mutual Funds - Mid Cap Value [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 627us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsMidCapValueMember
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Mutual Funds - Large Cap Blend [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,187us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsLargeCapBlendMember
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= us-gaap_PensionPlansDefinedBenefitMember		    
Mutual Funds - Large Cap Core [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 15,321us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsLargeCapCoreMember
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= msex_MutualFundsLargeCapCoreMember
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= us-gaap_PensionPlansDefinedBenefitMember		  
Mutual Funds - Foreign Small Mid Growth [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets   298us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsForeignSmallMidGrowthMember
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Mutual Funds - Foreign Large Core [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 989us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsForeignLargeCoreMember
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= msex_MutualFundsForeignLargeCoreMember
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= us-gaap_PensionPlansDefinedBenefitMember		  
Mutual Funds - Foreign Large Growth [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 449us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsForeignLargeGrowthMember
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= us-gaap_PensionPlansDefinedBenefitMember		  
Mutual Funds - Foreign Large Blend [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2,566us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsForeignLargeBlendMember
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= msex_MutualFundsForeignLargeBlendMember
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Mutual Funds - Pacific Asia/ex-Japan Stock [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets   157us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsPacificAsiaexJapanStockMember
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Mutual Funds - Diversified Emerging Markets [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 737us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= us-gaap_PensionPlansDefinedBenefitMember		  
Mutual Funds - Intermediate Term Bond [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 9,824us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsIntermediateTermBondMember
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= us-gaap_PensionPlansDefinedBenefitMember		 14,909us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsIntermediateTermBondMember
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= us-gaap_PensionPlansDefinedBenefitMember		  
Mutual Funds - Real Asset [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets   1,074us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsRealAssetMember
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Mutual Funds - World Bond [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 8,668us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_MutualFundsWorldBondMember
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Money Market Funds - Cash and Cash Equivalents [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 513us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Common Equity Securities - Non-Financial Services [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 280us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Common Equity Securities - Financial Services [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,656us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_EquitySecuritiesFinancialServicesMember
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Common Equity Securities - Utilities [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,504us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_EquitySecuritiesUtilitiesMember
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= us-gaap_PensionPlansDefinedBenefitMember		  
Common Equity Securities - Consumer Growth [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,123us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_EquitySecuritiesConsumerGrowthMember
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= us-gaap_PensionPlansDefinedBenefitMember		  
Common Equity Securities - Consumer Staples [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 459us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= us-gaap_PensionPlansDefinedBenefitMember		  
Common Equity Securities - Consumer Cyclicals [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 922us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_EquitySecuritiesConsumerCyclicalsMember
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= msex_EquitySecuritiesConsumerCyclicalsMember
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= us-gaap_PensionPlansDefinedBenefitMember		  
Common Equity Securities - Industrial Resources [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 155us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= us-gaap_PensionPlansDefinedBenefitMember		  
Common Equity Securities - Capital Equipment [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 453us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= msex_EquitySecuritiesCapitalEquipmentMember
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= us-gaap_PensionPlansDefinedBenefitMember		  
Common Equity Securities - Technology [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,328us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= us-gaap_PensionPlansDefinedBenefitMember		  
Common Equity Securities - Energy [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 712us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair Value, Level 1 [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 51,237us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair Value, Level 1 [Member] | Mutual Funds - Small Cap Core [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 261us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair Value, Level 1 [Member] | Mutual Funds - Small Cap Value [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 876us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair Value, Level 1 [Member] | Mutual Funds - Mid Cap Core [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,013us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair Value, Level 1 [Member] | Mutual Funds - Mid Cap Growth [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets   1,015us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair Value, Level 1 [Member] | Mutual Funds - Mid Cap Value [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 627us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair Value, Level 1 [Member] | Mutual Funds - Large Cap Blend [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1,187us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair Value, Level 1 [Member] | Mutual Funds - Large Cap Core [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 15,321us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair Value, Level 1 [Member] | Mutual Funds - Foreign Small Mid Growth [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets   298us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Fair Value, Level 1 [Member] | Mutual Funds - Foreign Large Core [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 989us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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Defined Benefit Plan Disclosure [Line Items]      
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Defined Benefit Plan Disclosure [Line Items]      
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Defined Benefit Plan Disclosure [Line Items]      
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Defined Benefit Plan Disclosure [Line Items]      
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Defined Benefit Plan Disclosure [Line Items]      
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Defined Benefit Plan Disclosure [Line Items]      
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Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
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Defined Benefit Plan Disclosure [Line Items]      
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Defined Benefit Plan Disclosure [Line Items]      
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Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
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Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
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Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets       
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Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets       
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Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
Fair Value, Level 3 [Member] | Common Equity Securities - Non-Financial Services [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
Fair Value, Level 3 [Member] | Common Equity Securities - Financial Services [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
Fair Value, Level 3 [Member] | Common Equity Securities - Utilities [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
Fair Value, Level 3 [Member] | Common Equity Securities - Consumer Growth [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
Fair Value, Level 3 [Member] | Common Equity Securities - Consumer Staples [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
Fair Value, Level 3 [Member] | Common Equity Securities - Consumer Cyclicals [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
Fair Value, Level 3 [Member] | Common Equity Securities - Industrial Resources [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
Fair Value, Level 3 [Member] | Common Equity Securities - Capital Equipment [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
Fair Value, Level 3 [Member] | Common Equity Securities - Technology [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets        
Fair Value, Level 3 [Member] | Common Equity Securities - Energy [Member]
      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets