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Net Income Per Share (Tables) | 12 Months Ended
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Dec. 31, 2017
Earnings Per Share [Abstract] |
Calculation of Net Income Per Share | The calculation of net income per share for the three years ended December 31, 2017 is reflected in the following table (in thousands, except per share amounts):
|  | Years Ended December 31,
|  | 2017 |  | 2016 |  | 2015
Net income |  | $ | 290,584 |  |  | $ | 343,389 |  |  | $ | 357,796 |
Basic: |  |  |  |  |  |
Weighted average shares |  | 124,152 |  |  | 127,991 |  |  | 131,749 |
Diluted: |  |  |  |  |  |
Weighted average shares |  | 124,152 |  |  | 127,991 |  |  | 131,749 |
Dilutive effect of potential common shares |  | 740 |  |  | 775 |  |  | 1,181 |
Diluted weighted average shares |  | 124,892 |  |  | 128,766 |  |  | 132,930 |
Net income per share: |  |  |  |  |  |
Basic |  | $ | 2.34 |  |  | $ | 2.68 |  |  | $ | 2.72 |
Diluted |  | $ | 2.33 |  |  | $ | 2.67 |  |  | $ | 2.69 |

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- Definition Tabular disclosure of an entity's basic and diluted earnings per share calculations, including a reconciliation of numerators and denominators of the basic and diluted per-share computations for income from continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
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