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STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract] |  |
Net income | $ 49,238 | $ 170,111
Postretirement benefits: |  |
Prior service cost | 92 | 0
Income tax benefit | (23) | 0
Total comprehensive income | $ 49,307 | $ 170,111

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- Definition Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=84228862&loc=d3e557-108580 + Details
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