Significant Accounting Policies - Inventories (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Mar. 31, 2016
Inventories
Crude oil	$ 146,857	$ 84,030
Natural gas liquids:
Propane	38,631	28,639
Butane	5,992	8,461
Other	6,035	6,011
Refined products:
Gasoline	193,051	80,569
Diesel	98,237	99,398
Renewables:
Ethanol	42,009	40,505
Biodiesel	21,410	11,953
Other	9,210	8,240
Total	$ 561,432	$ 367,806

EnergyRelatedInventoryBiodiesel

No definition available.

Name:	ngl_EnergyRelatedInventoryBiodiesel
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the carrying amount as of the balance sheet date of butane.

+ References

No definition available.

+ Details

Name:	ngl_EnergyRelatedInventoryButane
Namespace Prefix:	ngl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the carrying amount as of the balance sheet date of diesel.

+ References

No definition available.

+ Details

Name:	ngl_EnergyRelatedInventoryDiesel
Namespace Prefix:	ngl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

EnergyRelatedInventoryEthanol

+ References

No definition available.

+ Details

Name:	ngl_EnergyRelatedInventoryEthanol
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the carrying amount as of the balance sheet date of gasoline.

+ References

No definition available.

+ Details

Name:	ngl_EnergyRelatedInventoryGasoline
Namespace Prefix:	ngl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	ngl_EnergyRelatedInventoryNaturalGasLiquidsAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the carrying amount as of the balance sheet date of other natural gas liquids.

+ References

No definition available.

+ Details

Name:	ngl_EnergyRelatedInventoryOtherNaturalGasLiquids
Namespace Prefix:	ngl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	ngl_EnergyRelatedInventoryRefinedProductsAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

No definition available

+ References

No definition available.

+ Details

Name:	ngl_Ngl_EnergyRelatedInventoryRenewablesAbstract
Namespace Prefix:	ngl_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of petroleum or crude oil.

+ References

+ Details

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

- Definition

Carrying amount as of the balance sheet date of product derived from petroleum during the processing of oil or natural gas which is then used as a heat source or fuel.

+ References

+ Details

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

- Definition

Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6(a))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section 35
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=51655945&loc=d3e3927-108312

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765

+ Details

Name:	us-gaap_InventoryNet
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_InventoryNetAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount, net of valuation reserves and allowances, as of the balance sheet date of inventories not otherwise specified in the taxonomy.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.6)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 330
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB TOPIC 5.BB)
-URI http://asc.fasb.org/extlink&oid=27011343&loc=d3e100047-122729

+ Details

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