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Basis of Financial Reporting Revenue Disclosures (Details) $ in Thousands | Dec. 31, 2017 USD ($)
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Regulatory Liability [Domain] |
Cumulative Effect of New Accounting Principle in Period of Adoption | $ 12,100
Regulatory Liability [Domain] | Accounting Standards Update 2014-09 [Member] |
Cumulative Effect of New Accounting Principle in Period of Adoption | 12,107
Accounts Payable [Member] | Accounting Standards Update 2014-09 [Member] |
Cumulative Effect of New Accounting Principle in Period of Adoption | 8,747
Accrued Liabilities [Member] | Accounting Standards Update 2014-09 [Member] |
Cumulative Effect of New Accounting Principle in Period of Adoption | 22,794
Deferred Income Tax Charge [Member] | Accounting Standards Update 2014-09 [Member] |
Cumulative Effect of New Accounting Principle in Period of Adoption | $ 44,575

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