Significant Accounting Policies - Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Mar. 31, 2018
Inventories
Crude oil	$ 53,312	$ 77,351
Natural gas liquids:
Propane	92,328	38,910
Butane	30,855	12,613
Other	8,262	6,515
Refined products:
Gasoline	215,798	253,286
Diesel	125,565	113,939
Renewables:
Ethanol	38,911	38,093
Biodiesel	7,900	10,596
Total	$ 572,931	$ 551,303

Energy Related Inventory, Biodiesel

No definition available.

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- Definition

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

+ References

No definition available.

+ Details

Name:	ngl_EnergyRelatedInventoryButane
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Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	ngl_EnergyRelatedInventoryDiesel
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Balance Type:	debit
Period Type:	instant

- Definition

Energy Related Inventory Ethanol

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

Name:	ngl_EnergyRelatedInventoryGasoline
Namespace Prefix:	ngl_
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Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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- 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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- Definition

No definition available

+ References

No definition available.

+ Details

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- Definition

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

+ References

+ Details

Name:	us-gaap_EnergyRelatedInventoryPetroleum
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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
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Data Type:	xbrli:monetaryItemType
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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=68049868&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=82887183&loc=d3e6676-107765

+ Details

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- References

No definition available.

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