Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation (Details)

Share-Based Compensation (Details) (USD $)
9 Months Ended 0 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Restricted shares
Sep. 30, 2014
Mar. 06, 2014
2014 PSU Grants
Performance share units
Sep. 30, 2014
2014 PSU Grants
Performance share units
Share-Based Compensation            
Stock awards granted (in shares or units)     211,982   49,103  
Aggregate grant date fair value     $ 5,700,000   $ 1,700,000  
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            
Weighted average grant date fair value (in dollars per share)     $ 26.71     $ 35.09
Baseline value per common share (in dollars per share)           $ 26.52
Expected volatility of common shares (as a percent)           28.60%
Risk-free interest rate (as a percent)           0.66%
Other Share-based Compensation Additional Disclosures            
Shares vested (in shares)     165,076      
Weighted average fair value of shares vested (in dollars per share)     $ 29.01      
Aggregate intrinsic value of restricted common shares, forfeiture restrictions lapsed     4,400,000      
Exercised (in shares) 57,888 32,756   57,888    
Weighted average exercise price (in dollars per share)       $ 23.50    
Aggregate intrinsic value of options exercised (in dollars)       $ 214,000