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Stock-based Compensation - (Details) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 12 Months Ended
Aug. 07, 2014
Mar. 31, 2016
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Jul. 24, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Non-cash share compensation         $ 4,894 $ 3,798 $ 2,422  
2013 Plan | Restricted common shares                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares authorized 2,450,000             600,000
Number of additional shares authorized 1,850,000              
Granted (in shares)         155,306 162,522 152,987  
Share-based compensation, gross         $ 2,800 $ 2,600 $ 2,100  
Non-cash share compensation         3,600 2,900 2,200  
Unrecognized compensation expense         $ 1,200 $ 2,100 $ 2,400  
Initial estimated cumulative forfeiture rate (as a percent)         0.00%      
Grant date value (in dollars per share)         $ 17.96 $ 15.95 $ 13.79  
2013 Plan | Restricted common shares | Minimum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Vesting period         1 year 1 year 1 year  
2013 Plan | Restricted common shares | Maximum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Vesting period         3 years 3 years 3 years  
2013 Plan | Restricted Share Units                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Granted (in shares)       55,680        
Non-cash share compensation         $ 2,100 $ 900 $ 300  
Unrecognized compensation expense         $ 2,800 $ 1,600 $ 700  
Volatility   20.30% 20.70%          
2013 Plan | Restricted Share Units | Minimum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Volatility       18.80%        
2013 Plan | Restricted Share Units | Maximum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Volatility       34.20%        
2013 Plan | Performance based restricted stock units                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Percentage of shares awarded   20.00% 20.00%          
Grant date value (in dollars per share)   $ 26.33 $ 19.22 $ 16.94        
Grant date fair value (in dollars per share)   $ 17.67 $ 15.87 $ 13.47        
Officer | 2013 Plan | Restricted Share Units                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Granted (in shares)   104,553 75,250          
Vesting period       3 years 3 years      
Officer | 2013 Plan | Market Based RSU                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Percentage of shares awarded   80.00% 80.00% 80.00%        
Grant date value (in dollars per share)   $ 28.50 $ 20.06 $ 19.25        
Trustees | 2013 Plan | Restricted Share Units                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Granted (in shares)   36,784 40,957          
Vesting period         2 years      
Number of dividend equivalent included in award       1