Summary of Significant Accounting Policies (Details) - USD ($)	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Nov. 09, 2021	Dec. 31, 2020
Subsequent Event [Line Items]
Net loss	$ 23,213,000	$ 8,427,000	$ 9,688,000	$ 32,278,000	$ 50,712,000	$ 34,618,000	$ 41,328,000	$ 117,608,000
Fair value adjustment to warrants - Notes 11 and 18	812,000			(3,354,000)			10,956,000	(4,276,000)
Net cash used in operating activities							27,050,000	85,212,000
Cash	19,753,000			11,505,000			19,753,000	11,505,000		$ 56,363,000
Working capital	41,100,000						41,100,000
Liabilities	216,851,000			222,238,000			216,851,000	222,238,000		216,009,000
Accumulated deficit	562,087,000			$ 501,975,000			562,087,000	$ 501,975,000		$ 520,759,000
Debt, amount due in next 12 months	9,600,000						9,600,000
Sprott Credit Agreement
Subsequent Event [Line Items]
Minimum unrestricted cash	$ 10,000,000						$ 10,000,000
Sprott Credit Agreement | Subsequent event
Subsequent Event [Line Items]
Minimum unrestricted cash									$ 9,000,000