Annual report pursuant to Section 13 and 15(d)

Retirement And Savings Plan (Details)

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Retirement And Savings Plan (Details) (USD $)
12 Months Ended 15 Months Ended 21 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Mar. 31, 2010
Dec. 31, 2011
Retirement And Savings Plan [Abstract]          
Percentage of employee contribution 50.00%        
Contribution by employer, per dollar       $ 0.1 $ 0.25
Percentage of plan participant's deferrals       6.00% 6.00%
Matching contribution by employer $ 2,100,000 $ 1,400,000 $ 800,000