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Common Stock (Details)
12 Months Ended
Sep. 15, 2016
Aug. 12, 2016
shares
Feb. 15, 2008
$ / shares
shares
Dec. 31, 2016
shares
Dec. 31, 2015
shares
Dec. 31, 2014
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Stock split, conversion ratio   2        
Stock dividend payable (as a percent) 100.00%          
Total authorized shares before and after stock split (in shares)   40,000,000   40,000,000 40,000,000  
Stock Options            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Antidilutive stock options excluded from computation of earnings per share (in shares)       91,330 95,144 94,134
Employee benefit stock            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Common share purchase right dividend (in shares)     1      
Number of common shares each right is entitled to (in shares)     1      
Common share purchase right exercise price (in dollars per share) | $ / shares     $ 100.00