Annual report pursuant to Section 13 and 15(d)

Public Offering of Common Stock - Public Offering (Details)

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Public Offering of Common Stock - Public Offering (Details)
$ / shares in Units, $ in Thousands
 12 Months Ended
Nov. 16, 2017
USD ($)
$ / shares
shares
Oct. 13, 2016
USD ($)
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
Oct. 07, 2016
item
$ / shares
shares
Shares of common stock sold     38,900,875 34,350,329    
Par value of common stock | $ / shares     $ 0.01 $ 0.01    
Net proceeds from issuance of common stock | $     $ 132,964 $ 15,891 $ 18,767  
Offering expenses paid | $     $ 257 $ 228 $ 99  
October 2016 Offering            
Shares of common stock sold   2,683,334       2,333,334
Public offering price (in dollars per share) | $ / shares           $ 7.50
Net proceeds from issuance of common stock | $   $ 18,674        
October 2016 Offering | Directors and officers            
Shares of common stock sold           33,000
Number of directors and officers who purchased common stock | item           5
November 2017 Offering            
Shares of common stock sold 700,000          
Public offering price (in dollars per share) | $ / shares $ 21.00          
Net proceeds from issuance of common stock | $ $ 15,655          
ESSEX | November 2017 Offering            
Shares of common stock sold 1,000,000