Quarterly report pursuant to Section 13 or 15(d)

Share-Based Payments - Employee Activity Performance Shares (Details)

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Share-Based Payments - Employee Activity Performance Shares (Details) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense $ 1,677 $ 1,536 $ 3,329 $ 3,094
Key Employee Performance Share Based Plan [Member]
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Period of Share Price Performance Comparison to Peer Group     3 years  
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%  
Expected Stock Price Volatility Rate     32.50% 34.50%
Weighted Average Risk Free Interest Rate     0.70% 0.40%
Outstanding and non-vested, beginning of period (in shares) 74   88  
Grants in Period 0   23  
Additional Shares Awarded Based on Performance, Shares Issued in Period 0   19  
Shares Vested in Period 0   (56)  
Outstanding and non-vested, end of period (in shares) 74   74  
Outstanding and non-vested, weighted-average grant date fair value, beginning of period $ 44   $ 37  
Grants in Period, Weighted Average Grant Date Fair Value $ 0   $ 48  
Stock Issued During Period, Weighted Average Grant Date Fair Value $ 0   $ 30  
Vested in Period, Weighed-average grant date fair value $ 0   $ 30  
Outstanding and non-vested, weighted-average grant date fair value, end of period $ 44   $ 44  
Outstanding and non-vested, aggregate grant date fair value 3,279   3,279  
Share-based compensation expense 272 272 547 505
Tax benefit related to share-based expense 104 104 209 193
Unrecognized share-based compensation, net of estimated forfeitures $ 1,775 $ 1,740 $ 1,775 $ 1,740