Significant Accounting Policies - Income Taxes (Details)	12 Months Ended
Mar. 31, 2018
Income Tax Disclosure [Abstract]
Minimum percentage of qualifying income of non-taxable subsidiaries	90.00%

Represents the minimum percentage of qualifying income of non-taxable subsidiaries for each of the calendar years since the entity's initial public offering.

No definition available.

Name:	ngl_MinimumPercentageofQualifyingIncomeofNonTaxableSubsidiaries
Namespace Prefix:	ngl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration