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Significant Accounting Policies (Details 3) (USD $)
Sep. 30, 2014
Mar. 31, 2014
Dec. 02, 2013
Dec. 31, 2013
Jul. 02, 2014
Investments in Unconsolidated Entities          
Equity method ownership interest (as a percent)   50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage      
Carrying Value $ 482,644,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures $ 189,821,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures      
Glass Mountain          
Investments in Unconsolidated Entities          
Carrying Value 189,847,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_GlassMountainPipelineLLCMember
181,488,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_GlassMountainPipelineLLCMember
     
Fair value in excess of historical net book value 70,000,000ngl_EquityMethodInvestmentFairValueInExcessOfHistoricalNetBookValue
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_GlassMountainPipelineLLCMember
       
Ethanol production facility          
Investments in Unconsolidated Entities          
Carrying Value 9,361,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_EthanolProductionFacilityMember
8,333,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_EthanolProductionFacilityMember
     
Water Supply Company          
Investments in Unconsolidated Entities          
Carrying Value 15,026,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_WaterSupplyBusinessMember
       
BOSTCO          
Investments in Unconsolidated Entities          
Carrying Value 244,092,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_BostcoMember
       
Fair value in excess of historical net book value 24,000,000ngl_EquityMethodInvestmentFairValueInExcessOfHistoricalNetBookValue
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_BostcoMember
       
Frontera          
Investments in Unconsolidated Entities          
Carrying Value $ 24,318,000us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_FronteraBrownsvilleLLCMember
       
Gavilon Energy          
Investments in Unconsolidated Entities          
Equity method ownership interest (as a percent)     11.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= ngl_GavilonLLCMember
   
Gavilon Energy | Glass Mountain          
Investments in Unconsolidated Entities          
Equity method ownership interest (as a percent)     50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= ngl_GavilonLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_GlassMountainPipelineLLCMember
50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= ngl_GavilonLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_GlassMountainPipelineLLCMember
 
Gavilon Energy | Limited liability company          
Investments in Unconsolidated Entities          
Equity method ownership interest (as a percent)     11.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= ngl_GavilonLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_LimitedLiabilityCompanyMember
11.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= ngl_GavilonLLCMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= us-gaap_LimitedLiabilityCompanyMember
 
TransMontaigne | BOSTCO          
Investments in Unconsolidated Entities          
Equity method ownership interest (as a percent)         42.50%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= ngl_TransMontaigneIncMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_BostcoMember
TransMontaigne | Frontera          
Investments in Unconsolidated Entities          
Equity method ownership interest (as a percent)         50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_BusinessAcquisitionAxis
= ngl_TransMontaigneIncMember
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= ngl_FronteraBrownsvilleLLCMember