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Unaudited Quarterly Financial Data | 12 Months Ended
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Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract] |
Unaudited Quarterly Financial Data | Unaudited Quarterly Financial Data 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 |
| 2015 Quarter Ended
| March |  | June |  | September |  | December
Operating revenue | $ | 62,112 |  |  | 72,402 |  |  | 82,955 |  |  | 87,613 |
Operating income | 12,805 |  |  | 17,210 |  |  | 18,260 |  |  | 31,685 |
Net income | 4,695 |  |  | 7,461 |  |  | 9,534 |  |  | 16,192 |
Comprehensive income | 4,680 |  |  | 7,206 |  |  | 9,422 |  |  | 16,368 |
Earnings per share: |  |  |  |  |  |  |
—Basic | 0.23 |  |  | 0.37 |  |  | 0.47 |  |  | 0.79 |
—Diluted | 0.23 |  |  | 0.36 |  |  | 0.46 |  |  | 0.79 |
Market price range of stock: |  |  |  |  |  |  |
—High | 35.60 |  |  | 31.68 |  |  | 31.36 |  |  | 33.68 |
—Low | 30.09 |  |  | 28.68 |  |  | 27.73 |  |  | 27.64 |
Dividend per share | 0.20 |  |  | 0.19 |  |  | 0.20 |  |  | 0.19 |

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- Definition The entire disclosure for quarterly financial data. Includes, but is not limited to, tabular presentation of financial information for fiscal quarters, effect of year-end adjustments, and an explanation of matters or transactions that affect comparability of the information. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 270 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=68076893&loc=d3e1570-108306 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 270 -SubTopic 10 -Section 45 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=68064558&loc=d3e765-108305 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 270 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=68064558&loc=d3e725-108305 + Details
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