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 0 Months Ended 3 Months Ended 0 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Mar. 31, 2013
Options
Mar. 31, 2013
Restricted shares
Mar. 01, 2013
Performance share units
Mar. 31, 2013
Performance share units
Percentile_Rank
Mar. 01, 2013
2012 PSU Grants [Member]
Performance share units
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%  
Earned PSUs payout (as a percent of PSUs granted) on 50th percentile rank           100.00%  
Earned PSUs payout (as a percent of PSUs granted) on 25th percentile rank           50.00%  
Performance share units granted on percentile rank below 25th (as a percent)           0.00%  
The number of percentile ranks to fall between to earn interpolated PSUs between such percentile ranks, conditioned on the percentile rank exceeding 25%           2  
Performance period of the award (in years)           3 years  
Assumptions used to value stock awards              
Baseline value per common share (in dollars per share)           $ 25.85  
Expected volatility of common shares (as a percent)           29.50%  
Risk-free interest rate (as a percent)           0.33%  
Shares              
Stock awards granted (in shares or units)       117,960     69,579
Weighted Average Grant Date Fair Value              
Aggregate grant date fair value       $ 3,000,000 $ 1,900,000    
Weighted average grant date fair value (in dollars per share)       $ 25.85   $ 26.84  
Weighted average exercise price (in dollars per share)     $ 18.33        
Exercised (in shares) 16,453 5,667 16,453        
Aggregate intrinsic value of options exercised (in dollars)     129,000        
Other Share-based Compensation Additional Disclosures              
Aggregate intrinsic value of restricted common shares, forfeiture restrictions lapsed       $ 4,200,000      
Shares vested (in shares)       161,734      
Weighted average fair value of shares vested (in dollars per share)       $ 33.42