Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Regulatory Assets [Line Items]
Net Regulatory Assets	$ 152,279	$ 151,773
Less: current regulatory asset, net	11,368	16,064
Net regulatory assets, less current portion	140,911	135,709
Income tax temporary differences, net
Regulatory Assets [Line Items]
Regulatory assets:	10,139	10,139
Postretirement pensions and other medical benefits
Regulatory Assets [Line Items]
Regulatory assets:	109,795	109,795
Balancing and memorandum accounts, net
Regulatory Assets [Line Items]
Regulatory assets:	26,487	25,909
Other, net
Regulatory Assets [Line Items]
Regulatory assets:	$ 5,858	$ 5,930

The net amount of all regulatory assets less all regulatory liabilities 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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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.

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No definition available.

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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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- Definition

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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