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Share-Based Compensation and Capital Stock Summary Of Activity Related To Restricted Stock Grants (Details) - Restricted Stock [Member] - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Share-Based Compensation and Capital Stock [Line Items]        
Granted - shares 20,653 17,262 106,445 147,055
Weighted average grant date fair value per share (in dollars per share) $ 62.57 $ 44.62 $ 63.29 $ 46.46
Aggregate grant date fair value $ 1,292 $ 770 $ 6,737 $ 6,833
Restricted shares forfeited 3,664 2,964 8,442 4,296
Fair value of shares vested $ 1,054 $ 935 $ 11,739 $ 8,203
Minimum [Member]        
Share-Based Compensation and Capital Stock [Line Items]        
Vesting service period of shares granted 12 months 12 months 12 months 12 months
Maximum [Member]        
Share-Based Compensation and Capital Stock [Line Items]        
Vesting service period of shares granted 48 months 36 months 48 months 48 months