Revenues - Narrative (Details) - USD ($)	12 Months Ended			22 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Net product sales	$ 9,587,000	$ 0	$ 0
Collaboration revenue	4,056,000	$ 3,648,000	$ 0
Deferred revenue	10,800,000			$ 10,800,000
Revenue recognized				0
Other Current Assets
Disaggregation of Revenue [Line Items]
Deferred revenue	1,500,000			1,500,000
Fixed-price Contract
Disaggregation of Revenue [Line Items]
Payment due for collaborative agreement	20,000,000.0			20,000,000.0	$ 20,000,000.0
Payment made toward collaborative agreement				17,000,000.0
Variable Consideration Priced Contract | Upon Achievement of Regulatory Milestones
Disaggregation of Revenue [Line Items]
Additional amount that can be earned upon achievement of regulatory milestones	66,000,000.0			66,000,000.0
Variable Consideration Priced Contract | Upon Achievement of Net Sales Milestones
Disaggregation of Revenue [Line Items]
Additional amounts that could be earned by achievement of net sales milestones	$ 42,500,000			$ 42,500,000