Quarterly report pursuant to Section 13 or 15(d)

Long-term Incentive Plans (Details Textuals)

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Long-term Incentive Plans (Details Textuals) (USD $)
3 Months Ended 6 Months Ended 6 Months Ended 3 Months Ended 6 Months Ended
Jun. 30, 2011
Jun. 30, 2010
Jun. 30, 2011
Jun. 30, 2010
May 18, 2011
Jun. 30, 2011
Restricted Stock [Member]
Jun. 30, 2011
Restricted Stock Units [Member]
Jun. 30, 2010
Restricted Stock Units [Member]
Jun. 30, 2011
Restricted Stock Units [Member]
Jun. 30, 2010
Restricted Stock Units [Member]
Dec. 31, 2010
Restricted Stock Units [Member]
Unrecognized compensation cost, related to unvested restricted stock, total           $ 29,000,000          
Expected weighted average period to recognize compensation cost on restricted stock (in years)           2.0          
Vesting period for Restricted Stock Units                 3 years    
Compensation expense related to Restricted Stock Units             200,000 200,000 500,000 200,000  
Liabilities under Restricted Stock Units             600,000   600,000   200,000
Long Term Incentive Plans (Textuals) [Abstract]                      
Common Stock available for awards pursuant to the 2011 plan 11,750,000   11,750,000                
Number of additional shares of common stock available pursuant to the terms of the 2007 Plan         178,815            
Minimum vested period, restricted stock 3 years 3 years 3 years 3 years              
Maximum vested period, restricted stock 4 years 4 years 4 years 4 years              
Grant of restricted stocks under the Plans 67,198 53,919 900,000 1,100,000              
Weighted average grant price $ 19.90 $ 20.86 $ 22.16 $ 19.20              
Restricted stock, vested 55,128 53,539 900,000 700,000              
Fair value of additional restricted stock, vested $ 1,100,000 $ 1,100,000 $ 20,000,000 $ 13,000,000