Strategic Agreements - Summary of Collaborative Research and Development and Other Revenues Associated with Company's Collaborators or Counterparties (Parenthetical) (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenues	$ 2,212,000	$ 1,595,000
Agreement with Gilead [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenues	0	$ (465,000)
Net revenue reversal related to upfront license fee and milestone payment	465,000
Research and development expenses reimbursable	$ 197,000
Agreement with Gilead [Member] | License Fees [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount related to the milestone payment earned			$ 35,000,000.0