|**Common Stock Repurchase Plan (Tables)**               | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                          
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|**Common Stock Repurchase Plan [Abstract]**             |                                                                                                                                                                                                                                                                                                                                                                                                                         
|Information Relating to Repurchase Plan                 | Information relating to the Repurchase Plan is as follows:(in thousands)Three Months EndedMarch 31, 2018Common shares repurchased to treasury during period-Aggregate cost of shares repurchased during period$-(in thousands)March 31, 2018Total number of common shares authorized for repurchase$10,000Total number of common shares repurchased to date6,226Total number of shares that may yet be repurchased$3,774
|(in thousands)                                          |                                                                                                                                                                                                                                                                                                                                                                                                                         
|Common shares repurchased to treasury during period     |                                                                                                                                                                                                                                                                                                                                                                                                                         
|Aggregate cost of shares repurchased during period      |                                                                                                                                                                                                                                                                                                                                                                                                                         
|(in thousands)                                          |                                                                                                                                                                                                                                                                                                                                                                                                                         
|Total number of common shares authorized for repurchase |                                                                                                                                                                                                                                                                                                                                                                                                                         
|Total number of common shares repurchased to date       |                                                                                                                                                                                                                                                                                                                                                                                                                         
|Total number of shares that may yet be repurchased      |                                                                                                                                                                                                                                                                                                                                                                                                                         

X- DefinitionTabular disclosure of information related to common stock repurchase plan during the period.
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