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Stock-based Compensation - Summary of the Status of the Trust's Non-Vested Restricted Common Shares (Details) - 2013 Plan - Restricted common shares
6 Months Ended
Jun. 30, 2018
$ / shares
shares
Common Shares  
Non-vested at the beginning of the period (in shares) | shares 173,276
Granted (in shares) | shares 206,446
Vested (in shares) | shares (140,432)
Non-vested at the end of the period (in shares) | shares 239,290
Weighted Average Grant Date Fair Value  
Non-vested at beginning of period (in dollars per share) | $ / shares $ 19.36
Granted (in dollars per share) | $ / shares 14.87
Vested (in dollars per share) | $ / shares 19.63
Non-vested at end of period (in dollars per share) | $ / shares $ 15.33