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Employee Benefit Plans (Details) (USD $)
12 Months Ended
Dec. 31, 2011
years
Dec. 31, 2010
Dec. 31, 2009
Employee Benefit Plans [Abstract]      
Minimum eligible age for employees to defer a portion of their compensation, years 21    
Contribution made by company to match employee contribution $ 0.375 $ 0.75 $ 0.75
Employee contribution eligible for employer matching program 1.00 1.00 1.00
Maximum employer matching contribution, salary percentage   6.00% 6.00%
Expense made by company $ 7,400,000 $ 22,200,000 $ 18,900,000
Permitted deferment of compensation, percentage 75.00%    
Permitted deferment of annual bonus, percentage 100.00%