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 Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Employee Activity - Performance Shares [Line Items]      
Performance share vesting period 3 years    
Share-based compensation $ 5,971 $ 6,284 $ 6,754
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    
Median number of shares eligible for issuance 37,530    
Performance share price performance, minimum 30.00%    
Incremental number of issuable performance shares if Company share price outperforms peer group 75,060    
Minimum percentage of peer group by which Company share price must outperform before incremental performance shares are issued 90.00%    
Estimated fair value of performance shares $ 30.17    
Risk free rate of return 1.40%    
Number of years used in fair value calculation for share price volatility 3    
Expected stock price volatility 47.70%    
Share-based compensation 335    
Tax benefit related to share-based compensation expense 130    
Unrecognized compensation cost $ 798