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Shareholders' Equity - Common Stock, Distributions, Prospectus Supplement and Preferred Stock (Details)
 12 Months Ended
Mar. 13, 2017
USD ($)
shares
Mar. 08, 2017
shares
Mar. 07, 2017
$ / shares
shares
Dec. 31, 2017
vote
$ / shares
shares
Dec. 31, 2016
$ / shares
shares
Dec. 31, 2015
shares
Nov. 10, 2014
USD ($)
Class of Stock [Line Items]              
Number of votes per each share | vote       1      
Common stock, voting rights       one vote per share      
Minimum % of REIT taxable income to be paid as dividend annually       90.00%      
Issuance of common stock under prospectus supplement, shares 10,350,000   9,000,000        
Common stock, par value (in dollars per share) | $ / shares     $ 0.01 $ 0.01 $ 0.01    
Sale of stock, price per share (in dollars per share) | $ / shares     27.80        
Proceeds from issuance of common stock | $ $ 288,100,000            
Preferred stock, shares authorized       30,000,000 30,000,000    
Underwriters              
Class of Stock [Line Items]              
Sale of stock, price per share (in dollars per share) | $ / shares     $ 26.70        
Over-Allotment Option              
Class of Stock [Line Items]              
Proceeds from issuance of common stock | $ $ 37,600,000            
Over-Allotment Option | Underwriters              
Class of Stock [Line Items]              
Issuance of common stock under prospectus supplement, shares   1,350,000          
Option to exercise additional purchase of stock, term     30 days        
Prospectus Supplement              
Class of Stock [Line Items]              
Issuance of common stock under prospectus supplement, shares       0 0 0  
Maximum common stock value authorized under prospectus supplement | $             $ 150,000,000