Income Taxes - Narrative (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) ongoing_tax_audit	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Income Tax [Line Items]
Income tax expense (benefit)	$ 0	$ 0	$ 0
Amount of increase in valuation allowance	(111,000,000.0)
Accrual for interest or penalties on tax matters	$ 0	0	0
Number of ongoing tax audits | ongoing_tax_audit	0
Federal Tax Authority
Income Tax [Line Items]
Income tax expense (benefit)	$ 0	0	0
Canadian Federal
Income Tax [Line Items]
Scientific research and experimental development expenses deductible for income tax purposes	19,900,000	19,900,000	19,900,000
Net operating loss carry forwards (NOLs)	79,294,000
Canadian Provincial
Income Tax [Line Items]
Scientific research and experimental development expenses deductible for income tax purposes	21,600,000	$ 21,600,000	$ 21,600,000
Net operating loss carry forwards (NOLs)	78,673,000
US Federal
Income Tax [Line Items]
Net operating loss carry forwards (NOLs)	702,882,000
US Federal | Research Tax Credit Carryforward
Income Tax [Line Items]
Tax credit carryforward	29,700,000
US State
Income Tax [Line Items]
Net operating loss carry forwards (NOLs)	274,324,000
US State | Research Tax Credit Carryforward
Income Tax [Line Items]
Tax credit carryforward	$ 11,300,000