Summary of Significant Accounting Policies - Summary of Accounts Receivable (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 102	$ 176
Vifor [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	58	0
U.S. Food and Drug Administration [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 44	$ 176