Annual report pursuant to Section 13 and 15(d)

Public Offering of Common Stock (Details)

v3.10.0.1
Public Offering of Common Stock (Details)
$ / shares in Units, $ in Thousands
12 Months Ended
May 11, 2018
USD ($)
May 08, 2018
$ / shares
shares
Nov. 16, 2017
USD ($)
$ / shares
shares
Oct. 13, 2016
USD ($)
shares
Oct. 07, 2016
item
$ / shares
shares
Dec. 31, 2018
USD ($)
shares
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2016
USD ($)
Shares of common stock sold           38,900,875 34,350,329  
Proceeds from Issuance of Common Stock | $           $ 132,964 $ 15,891 $ 18,767
October 2016 Offering                
Shares of common stock sold       2,683,334 2,333,334      
Public offering price (in dollars per share) | $ / shares         $ 7.50      
Proceeds from Issuance of Common Stock | $       $ 18,674        
November 2017 Offering                
Shares of common stock sold     700,000          
Public offering price (in dollars per share) | $ / shares     $ 21.00          
Proceeds from Issuance of Common Stock | $     $ 15,655          
November 2017 Offering | ESSEX                
Shares of common stock sold     1,000,000          
May 2018 Offering                
Shares of common stock sold   3,000,000            
Public offering price (in dollars per share) | $ / shares   $ 41.00            
Proceeds from Issuance of Common Stock | $ $ 132,707              
Directors and officers | October 2016 Offering                
Shares of common stock sold         33,000      
Number of directors and officers who purchased common stock | item         5      
Underwriter | October 2016 Offering                
Shares of common stock sold         350,000      
Number Of Days To Underwriter To Purchase Additional Common Shares         30 days      
Underwriter | November 2017 Offering                
Shares of common stock sold     255,000          
Number Of Days To Underwriter To Purchase Additional Common Shares     30 days          
Underwriter | May 2018 Offering                
Shares of common stock sold   450,000            
Number Of Days To Underwriter To Purchase Additional Common Shares   30 days