Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation (Details)

v2.4.0.8
Share-Based Compensation (Details) (USD $)
6 Months Ended 0 Months Ended 6 Months Ended 0 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Mar. 01, 2013
Performance share units
Jun. 30, 2013
Performance share units
Percentile_Rank
Jun. 30, 2013
Restricted shares
Jun. 30, 2013
Options
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)         166,835   69,579
Weighted Average Grant Date Fair Value              
Aggregate grant date fair value     $ 1,900,000   $ 4,400,000    
Weighted average grant date fair value (in dollars per share)       $ 26.84 $ 26.46    
Exercised (in shares) 32,756 12,667       32,756  
Weighted average exercise price (in dollars per share)           $ 19.45  
Aggregate intrinsic value of options exercised (in dollars)           237,000  
Other Share-based Compensation Additional Disclosures              
Shares vested (in shares)         214,828    
Weighted average fair value of shares vested (in dollars per share)         $ 31.48    
Aggregate intrinsic value of restricted common shares, forfeiture restrictions lapsed         $ 5,700,000