|**Stock-Based Compensation (Tables)**                                                           | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                
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|**Disclosure of Compensation Related Costs, Share-based Payments [Abstract]**                   |                                                                                                                                                                                                                                                                                                                                                                                                                                
|Restricted shares, performance-based restricted share units and performance share unit activity | The following table presents activity for non-vested RSUs, performance-based RSUs and performance share units under the Plan in2015.Number of AwardsWeighted-Average Grant Date Fair ValueBalance as of January 1, 2015914,181$32.76Awards granted301,05741.04Awards vested(429,352)29.54Awards forfeited, canceled or expired(6,546)37.53Performance-based adjustment(44,077)37.47Balance as of December 31, 2015735,263$36.53
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|                                                                                                | Number of Awards                                                                                                                                                                                                                                                                                                                                                                                                               
|Balance as of January 1, 2015                                                                   | 914,181                                                                                                                                                                                                                                                                                                                                                                                                                        
|Awards granted                                                                                  | 301,057                                                                                                                                                                                                                                                                                                                                                                                                                        
|Awards vested                                                                                   | (429,352                                                                                                                                                                                                                                                                                                                                                                                                                       
|Awards forfeited, canceled or expired                                                           | (6,546                                                                                                                                                                                                                                                                                                                                                                                                                         
|Performance-based adjustment                                                                    | (44,077                                                                                                                                                                                                                                                                                                                                                                                                                        
|Balance as of December 31, 2015                                                                 | 735,263                                                                                                                                                                                                                                                                                                                                                                                                                        

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