Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax [Line Items]
Stock-based compensation	$ 2,940,000	$ 2,004,000
Valuation allowance	66,698,000	62,472,000
Net operating loss carryforwards	56,600,000	74,800,000
U.S. federal tax credits	3,100,000	1,300,000
Net operating loss deferred tax assets	18,792,000	21,005,000
Increase (decrease) in valuation allowance	4,200,000
Unrecognized tax benefits	0
Accrued interest or penalties related to unrecognized tax benefits	0
Reserves for uncertain income tax positions	0
United Kingdom
Income Tax [Line Items]
Net operating loss carryforwards	33,000,000
Restatement Adjustment
Income Tax [Line Items]
Stock-based compensation		10,800,000
Valuation allowance		$ 10,800,000
Aequus Biopharma, Inc
Income Tax [Line Items]
Net operating loss deferred tax assets	$ 9,900,000
Interest in majority-owned subsidiary	59.70%