Summary of Significant Accounting Policies (Schedule of Regulatory Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Regulatory Assets and Liabilities [Abstract]
Net Regulatory Assets	$ 103,625	$ 99,554
Current regulatory assets, net	26,910	0
Total regulatory assets, net, less current portion	76,715	99,554
Regulatory Liabilities	59,149	62,476
Postretirement pensions and other medical benefits [Member]
Regulatory Assets and Liabilities [Abstract]
Regulatory assets	66,233	68,556
Balancing and Memorandum Accounts [Member]
Regulatory Assets and Liabilities [Abstract]
Regulatory assets	34,413	27,925
Other Regulatory Assets [Member]
Regulatory Assets and Liabilities [Abstract]
Regulatory assets	2,979	3,073
Deferred Income Tax Charge
Regulatory Assets and Liabilities [Abstract]
Regulatory Liabilities	$ 59,149	$ 62,476

The net amount of all regulatory assets less all regulatory liabilities as of the end of the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

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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://fasb.org/us-gaap/role/ref/legacyRef
-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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