Investments and Fair Value Measurements (Details) - USD ($)	Dec. 31, 2020	Dec. 26, 2020	Mar. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	$ 70,003,000		$ 18,390,000
Total liabilities	0		0
Pfizer
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost share advance	138,800,000	$ 146,400,000
Money Market Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	3,000		11,348,000
Commercial Paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	65,501,000		7,042,000
Cash and cash equivalents	37,700,000		4,000,000.0
Marketable securities	27,800,000		3,000,000.0
Municipal Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	4,499,000
Quoted Market Prices for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	3,000		11,348,000
Quoted Market Prices for Identical Assets (Level 1) | Money Market Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	3,000		11,348,000
Quoted Market Prices for Identical Assets (Level 1) | Commercial Paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	0		0
Quoted Market Prices for Identical Assets (Level 1) | Municipal Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	0
Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	70,000,000		7,042,000
Significant Other Observable Inputs (Level 2) | Money Market Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	0		0
Significant Other Observable Inputs (Level 2) | Commercial Paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	65,501,000		7,042,000
Significant Other Observable Inputs (Level 2) | Municipal Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	4,499,000
Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	0		0
Significant Unobservable Inputs (Level 3) | Money Market Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	0		0
Significant Unobservable Inputs (Level 3) | Commercial Paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	0		$ 0
Significant Unobservable Inputs (Level 3) | Municipal Bonds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	$ 0