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

Regulatory Matters - Additional Information (Details) - FERC - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Sep. 30, 2017	Apr. 30, 2017	Mar. 31, 2017
Public Utilities, General Disclosures [Line Items]
Requested return on equity (percent)	10.00%
RECO
Public Utilities, General Disclosures [Line Items]
Requested rate increase, amount		$ 17.7	$ 11.8