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Employee and Non Employee Director Stock and Benefit Plans (Details 7) (ESPP, USD $)
1 Months Ended 12 Months Ended
Feb. 28, 1998
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
ESPP
       
Employee and non-employee director stock and benefit plans        
Discount rate at which employees can purchase shares (as a percent) 15.00%      
Share-based compensation expense   $ 451,000 $ 394,000 $ 765,000