Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity, Stock Options and Net Income per Share - Employee Activity - Performance Shares (Details)

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Shareholders' Equity, Stock Options and Net Income per Share - Employee Activity - Performance Shares (Details) (USD $)
In Thousands, except Per Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Employee Activity - Performance Shares [Line Items]      
Performance share vesting period 3 years    
Share-based compensation $ 6,050 $ 5,971 $ 6,284
Key Employee Performance Share Based Plan [Member]
     
Employee Activity - Performance Shares [Line Items]      
Performance share vesting period third    
Period of share price performance comparison to peer group 3 years    
Outstanding at beginning of year (shares) 38    
Granted (shares) 24 38  
Outstanding at end of year (shares) 62 38  
Weighted average grant date fair value of non-vested shares at beginning of year $ 30    
Weighted average fair value of performance shares $ 45 $ 30  
Weighted average grant date fair value non-vested shares at end of year $ 36 $ 30  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value 2,205 1,132  
Share-based compensation 699 335  
Tax benefit related to share-based compensation expense 269 130  
Unrecognized compensation cost $ 1,171    
Minimum percentage of peer group by which Company share price must outperform before incremental performance shares are issued 30.00%    
Percentage of Peer Group By Which Company Share Price Must Outperform Before Maximum Incremental Shares Are Issued 90.00%