Significant Accounting Policies, Regulatory Assets and Liabilities (Details) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($) ServiceLine	Dec. 31, 2016 USD ($)
Assets [Abstract]
Regulatory assets	$ 30,331	$ 33,027
Liabilities [Abstract]
Regulatory liabilities	24,495	4,640
Excess Accumulated Deferred Income Tax on Accelerated Depreciation [Member]
Liabilities [Abstract]
Regulatory liabilities	14,348	0
Income Taxes [Member]
Liabilities [Abstract]
Regulatory liabilities	$ 6,260	753
Income Taxes [Member] \| Minimum [Member]
Liabilities [Abstract]
Remaining recovery periods	1 year
Income Taxes [Member] \| Maximum [Member]
Liabilities [Abstract]
Remaining recovery periods	50 years
IRS TPR Catch-Up Deduction [Member]
Liabilities [Abstract]
Regulatory liabilities	$ 3,887	3,887
Income Taxes [Member]
Assets [Abstract]
Regulatory assets	18,564	20,609
Postretirement Benefits [Member]
Assets [Abstract]
Regulatory assets	$ 5,382	7,471
Postretirement Benefits [Member] \| Minimum [Member]
Assets [Abstract]
Remaining recovery period	5 years
Postretirement Benefits [Member] \| Maximum [Member]
Assets [Abstract]
Remaining recovery period	10 years
Unrealized Swap Losses [Member]
Assets [Abstract]
Regulatory assets	$ 2,172	2,264
Unrealized Swap Losses [Member] \| Minimum [Member]
Assets [Abstract]
Remaining recovery period	1 year
Unrealized Swap Losses [Member] \| Maximum [Member]
Assets [Abstract]
Remaining recovery period	12 years
Utility Plant Retirement Costs [Member]
Assets [Abstract]
Regulatory assets	$ 3,994	2,679
Remaining recovery period	5 years
Customer-Owned Lead Service Lines Replacements [Member]
Assets [Abstract]
Regulatory assets	$ 191	0
Term of tariff modification to replace customer-owned lead service lines connected to company-owned lead service lines	3 years
Number of lead customer-owned service lines to be replaced annually \| ServiceLine	400
Term of tariff modification to replace customer-owned lead service lines regardless of material used for company-owned service lines	9 years
Customer-Owned Lead Service Lines Replacements [Member] \| Minimum [Member]
Assets [Abstract]
Remaining recovery period	4 years
Customer-Owned Lead Service Lines Replacements [Member] \| Maximum [Member]
Assets [Abstract]
Remaining recovery period	6 years
Service Life Study Expenses [Member]
Assets [Abstract]
Regulatory assets	$ 23	4
Remaining recovery period	5 years
Rate Case Filing Expenses [Member]
Assets [Abstract]
Regulatory assets	$ 5	$ 0

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

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- Definition

The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 405
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394

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+ References

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Remaining recovery period of regulatory assets for which no return on investment during recovery period is provided, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 55
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82849221&loc=d3e44360-110383

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

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- Definition

Number of lead customer-owned service lines to be replaced annually whenever they are discovered.

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Term of tariff modification involving the replacement of lead customer-owned service lines that are discovered when the Company replaces its lead service lines, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Term of tariff modification involving the replacement of lead customer-owned service lines regardless of material used for company-owned service lines, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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