Quarterly report pursuant to Section 13 or 15(d)

Capital Stock - ATM Agreements - Additional Information (Details)

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Capital Stock - ATM Agreements - Additional Information (Details) - USD ($)
 1 Months Ended 3 Months Ended
Feb. 28, 2017
Mar. 31, 2018
Mar. 31, 2017
Nov. 12, 2015
Class Of Warrant Or Right [Line Items]        
Proceeds from issuance of common stock   $ 2,309,000 $ 5,380,000  
Common Stock [Member]        
Class Of Warrant Or Right [Line Items]        
Sale of shares 1,200,000      
2015 ATM Agreement [Member]        
Class Of Warrant Or Right [Line Items]        
Sales commission paid per transaction (in hundredths)   3.00%    
Maximum amount of shares can be issued       $ 75,000,000
Proceeds from issuance of common stock   $ 2,400,000 600,000  
Offering costs offset against proceeds upon sale of common stock   $ 100,000 $ 200,000  
Agreement expired date   2018-02    
2015 ATM Agreement [Member] | Common Stock [Member]        
Class Of Warrant Or Right [Line Items]        
Sale of shares   67,658 110,252