Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity (Deficit) - Public Offering (Details)

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Stockholders' Equity (Deficit) - Public Offering (Details)
 12 Months Ended
Nov. 16, 2017
USD ($)
$ / shares
shares
Oct. 13, 2016
USD ($)
shares
Oct. 07, 2016
item
$ / shares
shares
Aug. 26, 2015
USD ($)
$ / shares
shares
Feb. 13, 2015
USD ($)
$ / shares
shares
Feb. 05, 2015
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
$ / shares
shares
Dec. 31, 2015
USD ($)
Shares of common stock sold             34,350,329 33,008,865  
Par value of common stock | $ / shares             $ 0.01 $ 0.01  
Public offering price (in dollars per share) | $ / shares             $ 28.30 $ 9.00  
Net proceeds from issuance of common stock | $             $ 15,662,905 $ 18,668,092 $ 30,968,386
Offering expenses | $       $ 300,000          
February 2015 Offering                  
Shares of common stock sold         5,437,200 4,728,000      
Par value of common stock | $ / shares         $ 2.75 $ 0.01      
Public offering price (in dollars per share) | $ / shares           $ 2.75      
Number of days to underwriter to sell additional common shares           30 days      
Underwriting discounts, commissions and other estimated offering expenses | $         $ 15,000,000        
Offering expenses paid | $         $ 1,400,000        
August 2015 Offering                  
Shares of common stock sold       4,861,111          
Par value of common stock | $ / shares       $ 3.60          
Gross proceeds from issuance of common stock | $       $ 17,500,000          
October 2016 Offering                  
Shares of common stock sold     2,333,334            
Public offering price (in dollars per share) | $ / shares     $ 7.50            
Number of days to underwriter to sell additional common shares     30 days            
October 2016 Offering | Directors and officers                  
Shares of common stock sold     32,666            
Number of directors and officers who purchased common stock | item     5            
October 2016 Offering inclusive of over-allotment option                  
Shares of common stock sold   2,683,334              
Net proceeds from issuance of common stock | $   $ 18,670,000              
November 2017 Offering                  
Shares of common stock sold 700,000                
Number of days to underwriter to sell additional common shares 30 days                
Offering expenses | $ $ 15,650,000                
Underwriting Agreement                  
Shares of common stock sold 255,000 350,000 350,000     709,200      
ESSEX | November 2017 Offering                  
Shares of common stock sold 1,000,000                
Public offering price (in dollars per share) | $ / shares $ 21.00