Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity - Narrative (Details)

v3.20.4
Shareholders' Equity - Narrative (Details) - USD ($)
12 Months Ended
Jul. 27, 2020
Dec. 12, 2019
Sep. 13, 2019
Nov. 30, 2018
Mar. 29, 2018
Dec. 28, 2016
Feb. 14, 2014
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Class of Stock [Line Items]                      
Common stock, issued (shares)               126,725,000 111,798,000 85,500,000  
Common stock, outstanding (shares)               126,725,000 111,798,000 85,500,000  
Proceeds from offering         $ 15,000,000.0            
Share issuance costs               $ 12,268,000 $ 13,629,000    
Weighted average price per share (in usd per share)       $ 6.51              
Proceeds from exercise of warrants               $ 1,000 $ 6,988,000 $ 3,071,000  
Warrants                      
Class of Stock [Line Items]                      
Number of warrants outstanding               1,690,000 1,691,000 3,523,000  
Warrants exercised during period (in shares)               1,000   1,832,000  
Common Shares                      
Class of Stock [Line Items]                      
Common stock, outstanding (shares)               126,725,000 111,798,000 85,500,000 84,052,000
Share issuance costs               $ 12,268,000 $ 13,629,000    
July 2020 Public Offering                      
Class of Stock [Line Items]                      
Number of shares issued 13,300,000                    
Share price (in usd per share) $ 15.00                    
Proceeds from offering $ 200,000,000.0                    
Share issuance costs $ 12,300,000                    
Underwriting commissions percentage 6.00%                    
Underwriting commissions $ 12,000,000.0                    
Professional fees $ 268,000                    
December 2019 Public Offering                      
Class of Stock [Line Items]                      
Number of shares issued   12,800,000                  
Share price (in usd per share)   $ 15.00                  
Proceeds from offering   $ 191,700,000                  
Share issuance costs   $ 11,800,000                  
Underwriting commissions percentage   6.00%                  
Underwriting commissions   $ 11,500,000                  
Professional fees   $ 315,000                  
2019 Open Market Sale Agreement                      
Class of Stock [Line Items]                      
Number of shares issued         2,300,000            
Share price (in usd per share)         $ 6.40            
Share issuance costs         $ 640,000            
Underwriting commissions percentage         3.00%            
Underwriting commissions         $ 450,000            
Professional fees         $ 190,000            
Aggregate offering price     $ 40,000,000.0                
2018 Open Market Sale Agreement                      
Class of Stock [Line Items]                      
Number of shares issued       4,600,000              
Proceeds from offering       $ 30,000,000.0              
Share issuance costs       $ 1,200,000              
Underwriting commissions percentage       3.00%              
Underwriting commissions       $ 900,000              
Professional fees       270,000              
Aggregate offering price       $ 30,000,000.0              
2014 Private Offering                      
Class of Stock [Line Items]                      
Number of shares issued             18,900,000        
Subscription price per unit (in usd per share)             $ 2.7485        
Exercise price of warrants (in usd per share)             $ 3.2204        
2014 Private Offering | One Holder of Warrants                      
Class of Stock [Line Items]                      
Proceeds from exercise of warrants                 $ 1,500,000    
2014 Private Offering | Warrants                      
Class of Stock [Line Items]                      
Proceeds from offering             $ 52,000,000.0        
Warrant exercise period             5 years        
2014 Private Offering | Warrants | One Holder of Warrants                      
Class of Stock [Line Items]                      
Number of warrants outstanding                 464,000    
2014 Private Offering | Warrants | 2014 Warrant                      
Class of Stock [Line Items]                      
Number of shares called by each warrant             0.25        
2014 Private Offering | Warrants | 2014 Warrant Cashless Exercise                      
Class of Stock [Line Items]                      
Number of warrants outstanding                 1,300,000    
2014 Private Offering | Common Shares                      
Class of Stock [Line Items]                      
Number of shares called by each warrant             1        
Number of shares converted                 700,000    
2014 Private Offering | Common Shares | One Holder of Warrants                      
Class of Stock [Line Items]                      
Number of shares converted                 464,000    
2016 Bought Deal Public Offering                      
Class of Stock [Line Items]                      
Number of shares issued           12,800,000          
Subscription price per unit (in usd per share)           $ 2.25          
Exercise price of warrants (in usd per share)           $ 3.00     $ 3.00    
2016 Bought Deal Public Offering | Warrants                      
Class of Stock [Line Items]                      
Proceeds from offering           $ 28,800,000          
Share issuance costs           $ 655,000          
Warrant exercise period           5 years          
Exercise price of warrants (in usd per share)               $ 3.00      
Fair value of warrants           $ 7,200,000          
Proceeds from exercise of warrants               $ 2,000 $ 5,500,000    
Warrants exercised during period (in shares)               500      
2016 Bought Deal Public Offering | Warrants | 2014 Warrant                      
Class of Stock [Line Items]                      
Number of shares called by each warrant           0.50          
2016 Bought Deal Public Offering | Common Shares                      
Class of Stock [Line Items]                      
Number of shares called by each warrant           1