Commitments, Contingencies and Related Party Transactions - Additional Information (Details)		12 Months Ended
	May 22, 2019 USD ($) ft²	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Commitments And Contingencies [Line Items]
Rent expense		$ 100,000	$ 12,000
Operating lease liability		190,000
Insurance premium		1,200,000
Shanghai Pharmaceutical (USA) Inc.
Commitments And Contingencies [Line Items]
Amounts receivable		200,000
Agent
Commitments And Contingencies [Line Items]
Insurance commissions		100,000
Board of Directors
Commitments And Contingencies [Line Items]
Expense on services related to potential out-licensing or sale of technology		$ 3,500
San Diego, California | Office Space
Commitments And Contingencies [Line Items]
Rentable area | ft²	4,677
Lease expiration date	Mar. 31, 2021
Annual base rent	$ 166,000,000
Lease discount rate		10.00%
Operating lease liability		$ 200,000
Weighted average remaining lease term		1 year 3 months