Annual report pursuant to Section 13 and 15(d)

Capital Stock - ATM Agreements - Additional Information (Details)

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Capital Stock - ATM Agreements - Additional Information (Details) - USD ($)
 1 Months Ended 12 Months Ended
Dec. 18, 2018
Nov. 12, 2015
Dec. 31, 2018
Feb. 28, 2017
Dec. 31, 2018
Dec. 31, 2017
Class Of Warrant Or Right [Line Items]            
Proceeds from issuance of common stock         $ 6,063,000 $ 10,160,000
Offering costs offset against proceeds upon sale of common stock     $ 300,000      
Common Stock [Member]            
Class Of Warrant Or Right [Line Items]            
Sale of shares     285,689 1,200,000 354,000 1,849,000
2018 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 $ 30,000,000          
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