Fair Value Measurements - Summary of Changes in Estimated Fair Value of Financial Liabilities (Details) - USD ($) $ in Thousands		9 Months Ended
	Mar. 10, 2020	Sep. 30, 2020
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Reclassification of derivative liability to additional paid-in capital upon achievement of development milestone	$ 29,200
Level 3
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at December 31, 2019		$ 30,029
Changes in fair value		61,228
Payment of contingent consideration related to Humabs acquisition		(10,000)
Reclassification of derivative liability to additional paid-in capital upon achievement of development milestone		(29,245)
Balance at September 30, 2020		52,012
Level 3 | Contingent Consideration
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at December 31, 2019		17,580
Changes in fair value		44,432
Payment of contingent consideration related to Humabs acquisition		(10,000)
Balance at September 30, 2020		52,012
Level 3 | Derivative Liability
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at December 31, 2019		12,449
Changes in fair value		16,796
Reclassification of derivative liability to additional paid-in capital upon achievement of development milestone		$ (29,245)