Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax [Line Items]
Net operating losses with an indefinite life	$ 48,700,000
U.S. federal tax credits	7,300,000	$ 3,100,000
Net operating loss deferred tax assets	27,151,000	18,792,000
Increase (decrease) in valuation allowance	12,800,000
Unrecognized tax benefits	1,268,000	0	$ 0
Accrued interest or penalties related to unrecognized tax benefits	0
United Kingdom
Income Tax [Line Items]
Net operating loss carryforwards	40,900,000
Aequus Biopharma, Inc
Income Tax [Line Items]
Net operating loss deferred tax assets	$ 10,300,000
Interest in majority-owned subsidiary	59.70%
Domestic Tax Authority
Income Tax [Line Items]
Net operating loss carryforwards	$ 92,000,000	56,600,000
State and Local Jurisdiction
Income Tax [Line Items]
Net operating loss carryforwards	$ 12,700,000	$ 18,000,000