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Equity Incentive Plan - Additional Information (Details)
$ / shares in Units, $ in Millions
1 Months Ended 3 Months Ended 12 Months Ended
Mar. 02, 2018
$ / shares
shares
Mar. 01, 2018
$ / shares
shares
Jun. 01, 2017
officer
Mar. 01, 2017
$ / shares
shares
Jan. 28, 2016
$ / shares
shares
Jun. 01, 2015
$ / shares
shares
May 17, 2013
shares
Jan. 31, 2018
shares
Jan. 31, 2017
shares
Mar. 31, 2018
USD ($)
shares
Mar. 31, 2017
USD ($)
shares
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2016
shares
Dec. 31, 2015
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Compensation expense valuation of performance-based shares (in dollars per share) | $ / shares                           $ 21.21
Independent Trustees                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Common share issued as compensation for services performed (in shares)               21,670 23,980 6,491        
Equity Incentive Plan                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Number of shares authorized (in shares)             3,000,000              
Vesting period for share awards under equity             3 years              
2010 Equity Incentive Plan                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Number of trading days preceding the reporting date for which average of closing price of common shares is taken                       10 days    
Common shares available for issuance (in shares)                   1,405,529        
Time-based Restricted Stock Awards                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Vesting period for share awards under equity                   3 years        
Performance-based Restricted Stock Awards                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Vesting period for share awards under equity                   3 years        
Restricted Stock                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Unrecognized compensation costs | $                   $ 0.1   $ 0.1    
Weighted-average period for recognition of unrecognized compensation costs                   1 year 6 months        
Compensation expense, recognized | $                   $ 0.1 $ 0.2      
Number of shares, granted (in shares)                   0 5,000      
Long Term Incentive Plan Units                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Vesting period for share awards under equity           3 years                
Weighted-average period for recognition of unrecognized compensation costs                   2 years 5 months        
Compensation expense, recognized | $                   $ 0.7 $ 0.4      
Exchange ratio                   1        
Total unrecognized compensation cost related to LTIP Units | $                   $ 7.8   $ 4.4    
Number of shares, granted (in shares)                   244,917 223,922      
Initial award vesting rights, percentage           50.00%                
Annual award vesting rights after initial portion, percentage           25.00%                
Termination period upon change in control           18 months                
Distribution entitlement, percentage       10.00%   10.00%                
Long Term Incentive Plan Units | Awarded June 1, 2015                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Number of shares, granted (in shares)           183,300                
Grants in period, intrinsic value, amount per share (in dollars per share) | $ / shares           $ 14.13                
Long Term Incentive Plan Units | Officer                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Total number of awards (in shares)                   1,022,165        
Long Term Incentive Plan Units | Officer | Awarded In 2016                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Number of recipients (in officers) | officer     6                      
Awards vested to date, percentage                   66.00%        
Number of award in full parity (in shares)                         112,251  
Long Term Incentive Plan Units | Officer | Awarded In 2017                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Awards vested to date, percentage                   33.00%        
Number of award in full parity (in shares)                       223,922    
Long Term Incentive Plan Units | Officer | Awarded In 2018                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Number of award in full parity (in shares)                   593,948        
Long Term Incentive Plan Units, Time-Based | Awarded January 28, 2016                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Number of shares, granted (in shares)         72,966,000                  
Grants in period, intrinsic value, amount per share (in dollars per share) | $ / shares         $ 16.69                  
Long Term Incentive Plan Units, Time-Based | Awards March 1, 2017                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Number of shares, granted (in shares)       89,574,000                    
Grants in period, intrinsic value, amount per share (in dollars per share) | $ / shares       $ 18.53                    
Long Term Incentive Plan Units, Time-Based | Awards March 1, 2018                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Number of shares, granted (in shares) 97,968,000 97,968                        
Grants in period, intrinsic value, amount per share (in dollars per share) | $ / shares $ 16.83                          
Long Term Incentive Plan Units, Absolute TSR Component                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Portion of awards granted, percentage           60.00%                
Long Term Incentive Plan Units, Absolute TSR Component | Minimum                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Portion of awards to be granted if conditions are met, percentage           37.50%                
Total shareholder return threshold, percentage           25.00%                
Long Term Incentive Plan Units, Absolute TSR Component | Maximum                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Total shareholder return threshold, percentage           50.00%                
Long Term Incentive Plan Units, Relative TSR Component                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Portion of awards granted, percentage           40.00%                
Long Term Incentive Plan Units, Relative TSR Component | Minimum                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Portion of awards to be granted if conditions are met, percentage           37.50%                
Index percentile threshold, percentage           50.00%                
Long Term Incentive Plan Units, Relative TSR Component | Maximum                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Index percentile threshold, percentage           75.00%                
Payout Percentage                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Index percentile threshold, percentage   50.00%   50.00%                    
Payout Percentage | Minimum                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Index percentile threshold, percentage           50.00%                
Long Term Incentive Plan Units, Performance-Based | Awarded January 28, 2016                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Number of shares, granted (in shares)         39,285                  
Total shareholder return threshold, percentage         8.00%                  
Grants in period, intrinsic value, amount per share (in dollars per share) | $ / shares         $ 11.09                  
Annual vesting percentage         66.66%                  
Long Term Incentive Plan Units, Performance-Based | Awards March 1, 2017                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Number of shares, granted (in shares)       134,348                    
Grants in period, intrinsic value, amount per share (in dollars per share) | $ / shares       $ 19.65                    
Long Term Incentive Plan Units, Performance-Based | Awards March 1, 2017 | Minimum                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Percentage of target value to be paid out       50.00%                    
Long Term Incentive Plan Units, Performance-Based | Awards March 1, 2017 | Maximum                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Percentage of target value to be paid out       150.00%                    
Long Term Incentive Plan Units, Performance-Based | Awards March 1, 2018                            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                            
Number of shares, granted (in shares)   146,949                        
Grants in period, intrinsic value, amount per share (in dollars per share) | $ / shares   $ 17.02