Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation (Details)

v2.4.0.6
Share-Based Compensation (Details) (USD $)
3 Months Ended 1 Months Ended 3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Mar. 31, 2012
Options
Mar. 31, 2012
Restricted shares
Mar. 31, 2012
Performance share units
Mar. 31, 2012
Performance share units
Rank
Potential earned PSUs payout for defined levels of performance under awards            
Earned PSUs payout (as a percent of PSUs granted) on 75th or greater percentile rank         200.00% 200.00%
Earned PSUs payout (as a percent of PSUs granted) on 50th percentile rank         100.00% 100.00%
Earned PSUs payout (as a percent of PSUs granted) on 25th percentile rank         50.00% 50.00%
Performance share units granted on percentile rank below 25th (as a percent)         0.00% 0.00%
The number of percentile ranks to fall between to earn interpolated PSUs, conditioned on the percentile rank exceeding 25%           2
Assumptions used to value stock awards            
Baseline value per common share (in dollars per share)         $ 24.39 $ 24.39
Expected volatility of common shares (as a percent)           43.20%
Risk-free interest rate (as a percent)           0.41%
Shares            
Stock awards granted (in shares or units)       87,449 54,070  
Weighted Average Grant Date Fair Value            
Aggregate grant date fair value       $ 2,100,000 $ 1,800,000  
Grant date fair value (in dollars per share)       $ 24.39   $ 32.77
Options            
Exercised (in shares) (5,667) (24,667) (5,667)      
Exercise price range, options exercised (in dollars per share)     $ 14.54      
Aggregate intrinsic value (in dollars)     56,000      
Other Share-based Compensation Additional Disclosures            
Aggregate intrinsic value of restricted common shares, forfeiture restrictions lapsed       $ 6,200,000    
Restricted common shares, forfeiture restrictions lapsed (in shares)       251,985    
Weighted average grant date fair value of restricted common share, forfeiture restrictions lapsed (in dollars per share)       $ 31.93