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Summary of Significant Accounting Policies (Details Textuals) (USD $)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2011
Jun. 30, 2010
Jun. 30, 2011
Jun. 30, 2010
Dec. 31, 2010
Performance condition stock awards [Member]
Summary of Significant Accounting Policies (Textuals) [Abstract]          
Performance condition stock awards granted in 2010         $ 42.66
Additional Summary of Significant Accounting Policies (Textuals) [Abstract]          
Antidilutive securities excluded from computation of earnings per share 975,000 4,455,000 765,000 4,290,000