Annual report pursuant to Section 13 and 15(d)

Share-Based Compensation and Employee Benefit Plans (Details 4)

v2.4.0.6
Share-Based Compensation and Employee Benefit Plans (Details 4) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Performance share units
     
Share-Based Compensation      
Estimated pre-vesting forfeitures (as a percent) 0.00%    
Unrecognized compensation cost 2.3    
Expected weighted average period during which unrecognized compensation cost will be recognized 2 years    
Restricted shares
     
Share-Based Compensation      
Unrecognized compensation cost 6.8    
Expected weighted average period during which unrecognized compensation cost will be recognized 2 years    
Restricted shares | Minimum
     
Share-Based Compensation      
Estimated pre-vesting forfeitures (as a percent) 0.00% 0.00% 0.00%
Restricted shares | Maximum
     
Share-Based Compensation      
Estimated pre-vesting forfeitures (as a percent) 5.00% 4.00% 4.00%