Annual report pursuant to Section 13 and 15(d)

Share-Based Compensation and Other Compensation Matters (Details 6)

v3.6.0.2
Share-Based Compensation and Other Compensation Matters (Details 6)
12 Months Ended
Oct. 30, 2016
shares
Jul. 12, 2016
shares
May 30, 2016
shares
Mar. 05, 2015
shares
Dec. 31, 2016
USD ($)
Percentile_Rank
$ / shares
shares
Dec. 31, 2015
USD ($)
$ / shares
shares
Dec. 31, 2014
USD ($)
$ / shares
shares
May 31, 2010
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Decrease in tax benefit from share-based compensation | $         $ 331,000 $ 513,000 $ 3,000  
Executive transition costs | $         $ 6,500,000      
Stock Options [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Expiration period         10 years      
Restricted shares [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Unrecognized compensation cost | $         $ 5,600,000      
Expected weighted average period during which unrecognized compensation cost will be recognized         3 years      
Aggregate intrinsic value of vested shares | $         $ 5,400,000 $ 4,900,000 $ 4,900,000  
Vested (in shares) | shares         (215,983) (202,781) (182,213)  
Vested (in dollars per share) | $ / shares         $ 27.19 $ 26.07 $ 28.56  
Restricted shares [Member] | Minimum [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Estimated pre-vesting forfeitures (as a percent)         0.00%      
Restricted shares [Member] | Maximum [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Estimated pre-vesting forfeitures (as a percent)         5.00%      
Performance share units [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Estimated pre-vesting forfeitures (as a percent)         0.00%      
Unrecognized compensation cost | $         $ 873,000      
Expected weighted average period during which unrecognized compensation cost will be recognized         2 years      
Performance period of the award         3 years      
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      
Deferred Share Award [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Estimated pre-vesting forfeitures (as a percent)         0.00%      
Unrecognized compensation cost | $         $ 241,000      
Aggregate intrinsic value of vested shares | $         $ 322,000 $ 413,000    
Vested (in shares) | shares         (12,028) (15,485)    
Vested (in dollars per share) | $ / shares         $ 26.70 $ 26.77    
Options [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Aggregate intrinsic value of options exercised | $           $ 300,000 $ 225,000  
Amended and Restated 2008 Omnibus Equity and Incentive Plan [Member] | Maximum [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of common shares of beneficial interest authorized to be issued | shares               5,900,000.0
2012 PSU Grants [Member] | Performance share units [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Shares issued for PSU Awards Vested in Period (in shares) | shares       40,309        
2013 and 2014 PSU Grants [Member] | Performance share units [Member] | Former Chief Financial Officer [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Shares issued for PSU Awards Vested in Period (in shares) | shares       15,289        
2014 and 2015 Performance Share Unit Grants [Member] | Performance share units [Member] | Executive Vice President [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Shares issued for PSU Awards Vested in Period (in shares) | shares     10,326          
2014 and 2015 Performance Share Unit Grants [Member] | Performance share units [Member] | Chief Executive Officer [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Shares issued for PSU Awards Vested in Period (in shares) | shares   20,569            
2014, 2015 and 2016 Performance Share Unit Grants [Member] | Performance share units [Member] | General Counsel [Member]                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Shares issued for PSU Awards Vested in Period (in shares) | shares 2,248