Fair Value Measurements - Narrative (Details) - USD ($)	Mar. 31, 2021	Dec. 26, 2020	Mar. 31, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cost share advance	$ 121,862,000		$ 0
Fair Value, Nonrecurring
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total assets	0		0
Total liabilities			$ 0
Pfizer
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cost share advance		$ 146,400,000
Pfizer | Fair Value, Nonrecurring
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cost share advance	$ 146,400,000