Quarterly report pursuant to Section 13 or 15(d)

Share-Based Compensation and Other Compensation Matters (Details)

v3.8.0.1
Share-Based Compensation and Other Compensation Matters (Details)
 9 Months Ended
Aug. 23, 2017
USD ($)
$ / shares
shares
Aug. 22, 2017
$ / shares
Feb. 07, 2017
shares
Jan. 01, 2017
USD ($)
employee
Percentile_Rank
$ / shares
shares
Sep. 30, 2017
USD ($)
$ / shares
shares
Other Share-based Compensation Additional Disclosures          
Options exercised in period (in shares or units)         5,000
Restricted shares          
Share-Based Compensation          
Stock awards granted (in shares or units)         230,635
Aggregate grant date fair value | $         $ 7,800,000
Assumptions used to value stock awards          
Weighted average grant date fair value (in dollars per share) | $ / shares         $ 33.96
Other Share-based Compensation Additional Disclosures          
Shares vested (in shares)         148,401
Weighted average fair value of shares vested (in dollars per share) | $ / shares         $ 26.18
Aggregate intrinsic value of awards upon vesting | $         $ 5,000,000
Deferred share awards          
Share-Based Compensation          
Stock awards granted (in shares or units)         10,032
Aggregate grant date fair value | $         $ 326,000
Assumptions used to value stock awards          
Weighted average grant date fair value (in dollars per share) | $ / shares         $ 32.47
Other Share-based Compensation Additional Disclosures          
Shares vested (in shares)         15,590
Weighted average fair value of shares vested (in dollars per share) | $ / shares         $ 26.89
Aggregate intrinsic value of awards upon vesting | $         $ 508,000
Options          
Other Share-based Compensation Additional Disclosures          
Options exercised in period (in shares or units)         5,000
Options exercised weighted average exercise price (in dollars per share) | $ / shares         $ 29.98
Intrinsic value of options exercised | $         $ 18,000
2017 PSU Grants | Performance share units          
Share-Based Compensation          
Stock awards granted (in shares or units) 2,826     36,525  
Aggregate grant date fair value | $       $ 1,400,000  
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% | Percentile_Rank       2  
Assumptions used to value stock awards          
Performance period of the award       3 years  
Negative TSR Modifier payout percentage 100.00%        
Incremental value of awards | $ $ 12,000        
Weighted average grant date fair value (in dollars per share) | $ / shares $ 46.39 $ 49.66   $ 38.43  
Baseline value per common share (in dollars per share) | $ / shares $ 33.40     $ 31.22  
Expected volatility of common shares (as a percent) 18.70%     19.00%  
Risk-free interest rate (as a percent) 1.36%     1.47%  
2017 PSU Grants | Performance share units | Executive Officer [Member]          
Share-Based Compensation          
Number of employees affected | employee       3  
2014 PSU Grants | Performance share units | Chief Executive Officer          
Other Share-based Compensation Additional Disclosures          
Shares issued (in shares)     9,763    
Percentage of target     100.00%