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, 2013
Dec. 31, 2012
Dec. 31, 2011
Employee Activity - Performance Shares [Line Items]      
Share-based compensation $ 6,178 $ 6,050 $ 5,971
Key Employee Performance Share Based Plan [Member]
     
Employee Activity - Performance Shares [Line Items]      
Share-based awards, vesting period 3 years    
Period of share price performance comparison to peer group   3 years  
Outstanding at beginning of year (shares) 62 38  
Granted (shares) 26 24 38
Outstanding at end of year (shares) 88 62 38
Weighted average grant date fair value of non-vested shares at beginning of year $ 36 $ 30  
Weighted average fair value of performance shares $ 40 $ 45 $ 30
Weighted average grant date fair value non-vested shares at end of year $ 37 $ 36 $ 30
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Granted in Period, Total Fair Value 3,278 2,205 1,132
Share-based compensation 1,055 699 335
Tax benefit related to share-based compensation expense 402 269 130
Unrecognized compensation cost $ 1,190    
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%