Commitments and Contingencies - Joint-Owned Utility Poles (Details) - Jointly owned utility plant	12 Months Ended
Dec. 31, 2017 county item
Loss Contingencies [Line Items]
Number of counties \| county	3
Number of joint pole owners \| item	1
Maximum
Loss Contingencies [Line Items]
Number of counties \| county	4
Dispute resolution process
Loss Contingencies [Line Items]
Number of utilities \| item	1

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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Balance Type:	na
Period Type:	duration