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Unaudited Quarterly Financial Data (Tables) | 12 Months Ended
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Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract] |
Schedule of Quarterly Financial Information | Summarized quarterly financial data is as follows:
| 2016 Quarter Ended
| March |  | June |  | September |  | December
Operating revenue | $ | 61,112 |  |  | 86,944 |  |  | 112,344 |  |  | 79,306 |
Operating income | 10,581 |  |  | 29,800 |  |  | 36,346 |  |  | 16,389 |
Net income | 3,378 |  |  | 16,775 |  |  | 18,959 |  |  | 13,727 |
Comprehensive income | 3,908 |  |  | 15,520 |  |  | 18,790 |  |  | 13,834 |
Earnings per share: |  |  |  |  |  |  |
—Basic | 0.17 |  |  | 0.82 |  |  | 0.93 |  |  | 0.67 |
—Diluted | 0.16 |  |  | 0.82 |  |  | 0.92 |  |  | 0.67 |
Market price range of stock: |  |  |  |  |  |  |
—High | 37.50 |  |  | 39.38 |  |  | 46.66 |  |  | 56.69 |
—Low | 29.35 |  |  | 32.66 |  |  | 38.13 |  |  | 42.19 |
Dividend per share | 0.20 |  |  | 0.20 |  |  | 0.20 |  |  | 0.20 |

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- Definition Tabular disclosure of quarterly financial data. Includes, but is not limited to, financial information for fiscal quarters, cumulative effect of a change in accounting principle and earnings per share data. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 270 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a)-(j) -URI http://asc.fasb.org/extlink&oid=68076893&loc=d3e1280-108306 + Details
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