Equity - Equity-Based Incentive Compensation - Performance Awards (Details) $ in Thousands	3 Months Ended
Jun. 30, 2017 USD ($) shares
Performance awards
Equity-Based Incentive Compensation
Performance award activity (in units) \| shares	0
Estimated equity-based compensation expense
2018 (nine months)	$ 4,127
2019	3,232
2020	655
Total	$ 8,014
Restricted units
Estimated equity-based compensation expense
Number of shares available for grant \| shares	2,400,000
Vesting On July 1, 2017 \| Performance awards
Equity-Based Incentive Compensation
Units vested and issued (in units) \| shares	0

No definition available.

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

- Definition

Represents the amount of expense expected to be recognized during in the remainder of the fiscal year following the latest fiscal year arising from the equity-based compensation arrangements.

+ References

No definition available.

+ Details

Name:	ngl_AllocatedShareBasedCompensationExpenseRemainderOfFiscalYear
Namespace Prefix:	ngl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the amount of total expense expected to be recognized from the equity-based compensation arrangements.

+ References

No definition available.

+ Details

Name:	ngl_AllocatedShareBasedCompensationExpenseTotal
Namespace Prefix:	ngl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the amount of expense expected to be recognized during the third fiscal year following the latest fiscal year arising from the equity-based compensation arrangements.

+ References

No definition available.

+ Details

Name:	ngl_AllocatedShareBasedCompensationExpenseYearThree
Namespace Prefix:	ngl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the amount of expense expected to be recognized during the second fiscal year following the latest fiscal year arising from the equity-based compensation arrangements.

+ References

No definition available.

+ Details

Name:	ngl_AllocatedShareBasedCompensationExpenseYearTwo
Namespace Prefix:	ngl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Increase (decrease) in the number of shares under non-option equity instrument agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=ngl_VestingOn1July2017Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: