Acquisitions - Acquisition of Customers from Perigee (Details) - Perigee - Customer Relationships kWh in Millions, $ in Millions	1 Months Ended
Apr. 30, 2017 USD ($) kWh
Business Acquisition [Line Items]
Residential customer equivalent (in kwh) \| kWh	440
Contract purchase price \| $	$ 7.5

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.

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