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.

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

Minnesota Public Utilities Commission (Details 2) - MNPUC [Member] - Natural gas cost tariff [Member] - USD ($)	Oct. 06, 2017	Dec. 21, 2016
Public Utilities, General Disclosures [Line Items]
Public utilities, requested rate increase (decrease), amount		$ 456,000
Subsequent event [Member]
Public Utilities, General Disclosures [Line Items]
Public utilities, approved rate increase (decrease), amount	$ 456,000