| **Earnings per share**            | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
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| **Earnings Per Share [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
| Earnings Per Share                | EARNINGS PER SHAREBasic earnings per share is computed by dividing net earnings by the weighted-average number of common shares outstanding for the period. Diluted earnings per share is similarly computed, except that the denominator includes the effect, using the treasury stock method, of unvested restricted stock, outstanding SARs, stock options, Convertible Notes and shares held pursuant to our non-employee director deferred compensation plan, if including such potential shares of common stock is dilutive.The following table presents a reconciliation of the weighted-average diluted shares outstanding: Three Months Ended June 30, Six Months Ended June 30, 2015 2014 2015 2014 (in thousands)        Weighted-average common shares outstanding - basic40,035 35,762 38,202 35,726Weighted-average common shares and equivalents outstanding - diluted40,035 35,762 38,202 35,726        We reported a net loss for the three and six months ended June 30, 2015 and 2014, respectively. As a result, our basic and diluted weighted-average common shares outstanding were the same as the effect of the common share equivalents was anti-dilutive.The following table presents the weighted-average common share equivalents excluded from the calculation of diluted earnings per share due to their anti-dilutive effect: Three Months Ended June 30, Six Months Ended June 30, 2015 2014 2015 2014 (in thousands)        Weighted-average common share equivalents excluded from diluted earnings       per share due to their anti-dilutive effect:       Restricted stock871 896 832 859SARs108 92 89 96Stock options4 4 4 4Non-employee director deferred compensation6 5 6 5Convertible notes677 881 523 758Total anti-dilutive common share equivalents1,666 1,878 1,454 1,722        In November 2010, we issued our Convertible Notes, which give the holders the right to convert the aggregate principal amount into 2.7 million shares of our common stock at a conversion price of $42.40 per share. The Convertible Notes could be included in the diluted earnings per share calculation using the treasury stock method if the average market share price exceeds the $42.40 conversion price during the period presented. Shares issuable upon conversion of the Convertible Notes were excluded from the diluted earnings per share calculation for the three and six months ended June 30, 2015 and 2014, respectively, as the effect would be anti-dilutive to our earnings per share. |

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