Summary of Significant Accounting Policies Components of Addition to Net Utility Plant (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of Significant Accounting Policies [Abstract]
Company Financed Additions to Utility Plant	$ 54,504	$ 51,543	$ 66,339
Increase (Decrease) in Allowance for Equity Funds Used During Construction	465	774	1,198
Subtotal - Utility Plant Increase to Rate Base	54,969	52,317	67,537
Advances from Others for Construction	2,526	1,479	350
Property, Plant and Equipment, Additions	$ 57,495	$ 53,796	$ 67,887

The increase (decrease) during the reporting period in the capitalized cost of equity (based on assumed rate of return) and / or borrowed funds (based on interest rate) used to finance construction of regulated assets, which is expected to be recovered through rate adjustments. As a result of this capitalization, net income is increased. This element pertains to certain regulated industries, such as public utilities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration