| **Earnings (loss) per share**     | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
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| **Earnings Per Share [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
| Earnings Per Share                | Note B. Earnings Per ShareEarnings per share is based on the weighted average number of outstanding common shares.  Basic earnings (loss) per share excludes the impact of dilutive securities and is computed by dividing Net income (loss) by the weighted average number of common shares outstanding for the period.  Diluted earnings (loss) per share reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock.For the three and six months ended June 30, 2013, approximately 407 thousand and 446 thousand potential shares attributable to exercises under stock-based employee compensation plans were included in the calculation of diluted earnings per share.  For those same periods, approximately 114 thousand and 478 thousand potential shares attributable to exercises under stock-based employee compensation plans were not included in the calculation of diluted earnings per share because the effect would have been antidilutive.For the three and six months ended June 30, 2012, approximately 410 thousand and 368 thousand potential shares attributable to exercises under stock-based employee compensation plans were included in the calculation of diluted earnings per share.  For those same periods, approximately 622 thousand and 735 thousand potential shares attributable to exercises under stock-based employee compensation plans were not included in the calculation of diluted earnings per share because the effect would have been antidilutive. |

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| - Definition
The entire disclosure for earnings per share.
+ References
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