Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity - Narrative (Details)

Shareholders' Equity - Narrative (Details) - USD ($)								1 Months Ended	12 Months Ended
Shareholders' Equity - Narrative (Details) - USD ($)	Nov. 19, 2021	Jul. 27, 2020	Dec. 12, 2019	Sep. 13, 2019	Mar. 29, 2018	Dec. 28, 2016	Feb. 14, 2014	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Common stock, outstanding (shares)								141,600,000	141,600,000	126,725,000	111,800,000
Common stock, issued (shares)								141,600,000	141,600,000	126,725,000	111,800,000
Proceeds from offering					$ 15,000,000
Proceeds from exercise of warrants									$ 365,000	$ 1,000	$ 6,988,000
Warrants exercised during period (in shares)									1,700,000	500
Warrants
Class of Stock [Line Items]
Number of warrants outstanding								0	0	1,690,000	1,691,000
Warrants exercised during period (in shares)									1,684,000		1,000
Warrants expired, in shares									6,000
Common Shares
Class of Stock [Line Items]
Common stock, outstanding (shares)								141,600,000	141,600,000	126,725,000	111,798,000	85,500,000
Share issuance costs									$ 5,616,000	$ 12,268,000	$ 13,629,000
November 2021 Open Market Sale Agreement
Class of Stock [Line Items]
Aggregate offering price	$ 250,000,000
Number of shares issued	10,200,000
Weighted average price per share (in usd per share)	$ 19.90
Proceeds from offering								$ 202,400,000
Share issuance costs	$ 5,600,000
Underwriting commissions percentage	3.00%
Underwriting commissions	$ 5,300,000
Professional fees	$ 300,000
July 2020 Public Offering
Class of Stock [Line Items]
Number of shares issued		13,300,000
Proceeds from offering		$ 200,000,000
Share issuance costs		$ 12,300,000
Underwriting commissions percentage		6.00%
Underwriting commissions		$ 12,000,000
Professional fees		$ 300,000
Share price (in usd per share)		$ 15.00
December 2019 Public Offering
Class of Stock [Line Items]
Number of shares issued			12,800,000
Proceeds from offering			$ 191,700,000
Share issuance costs			$ 11,800,000
Underwriting commissions percentage			6.00%
Underwriting commissions			$ 11,500,000
Professional fees			$ 300,000
Share price (in usd per share)			$ 15.00
2019 Open Market Sale Agreement
Class of Stock [Line Items]
Aggregate offering price				$ 40,000,000
Number of shares issued					2,300,000
Weighted average price per share (in usd per share)					$ 6.40
Share issuance costs					$ 640,000
Underwriting commissions percentage					3.00%
Underwriting commissions					$ 450,000
Professional fees					$ 190,000
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
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	$ 3.00	$ 3.00	$ 3.00
Proceeds from exercise of warrants									$ 300,000	$ 2,000	$ 5,500,000
Warrants expired, in shares									6,000
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
Number of warrants outstanding								1,600,000	1,600,000
Fair value of warrants						$ 7,200,000
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
Number of shares converted									1,300,000