Rate Regulation - Rate Case Filings (Details) $ in Millions	Oct. 01, 2016 USD ($)
Filing for Gas Cost Increase, Effective November 2016 \| PSCU \| Subsequent Event
Public Utilities, General Disclosures [Line Items]
Amount of gas cost increase	$ 8.6

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.

No definition available.

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