Quarterly report pursuant to Section 13 or 15(d)

Capitalization and Equity Structure - Additional Information (Details)

v3.19.1
Capitalization and Equity Structure - Additional Information (Details) - USD ($)
1 Months Ended 3 Months Ended 12 Months Ended
Jan. 30, 2019
Aug. 21, 2018
Dec. 31, 2015
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Mar. 08, 2019
Mar. 07, 2019
Dec. 31, 2018
Sep. 30, 2017
Class of Stock [Line Items]                      
Common stock, shares authorized (in shares)       141,429,000           141,429,000  
Preferred Stock, shares authorized (in shares)       10,000,000           10,000,000  
Common stock, shares outstanding (in shares)       67,529,000           62,963,000  
Common stock, shares issued (in shares)       67,529,000           62,963,000  
Preferred stock, shares outstanding (in shares)       0           0  
Preferred stock, shares issued (in shares)       0           0  
Proceeds from issuance of common stock and warrants, net       $ 2,313,000              
Loss on modification of warrants       $ 257,000 $ 0            
2015 Warrants                      
Class of Stock [Line Items]                      
Exercise price (in dollars per share)       $ 2.75              
Warrants issued (in shares)     2,122,000                
Information Agent Warrants                      
Class of Stock [Line Items]                      
Warrants called (in shares)                     200,000
Exercise price (in dollars per share)       $ 1.5             $ 1.5
2015 Warrants, Amendment                      
Class of Stock [Line Items]                      
Exercise price (in dollars per share)               $ 2.75 $ 3.74    
Common Stock                      
Class of Stock [Line Items]                      
Number of shares sold (in shares) 3,067                    
Price per share sold (in dollars per share) $ 1.63                    
Amount received from sale of shares $ 5,000,000                    
Common Stock | At-The-Market Offering                      
Class of Stock [Line Items]                      
Aggregate value of offering   $ 25,000,000                  
Number of shares sold (in shares)       1,294,000              
Price per share sold (in dollars per share)       $ 1.85              
Value of stock available for issuance       $ 17,734,000              
Warrant                      
Class of Stock [Line Items]                      
Warrants exercised (in shares)           30,000 488,000