Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Examination [Line Items]
Income tax expense	$ 0	$ 0
Increase (decrease) in net valuation allowance	(10,900,000)	300,000
Unrecognized tax benefits	1,439,000	1,128,000	$ 1,006,000
Unrecognized tax-related penalties or interest	$ 0	0
Minimum
Income Tax Examination [Line Items]
Percentage of change In ownership for operating loss carryforward	50.00%
Period for change in ownership percentage	3 years
California
Income Tax Examination [Line Items]
Net operating loss carryforwards, valuation allowance	$ 197,500,000
Deferred tax assets, net operating loss carryforwards derecognized amount	13,800,000
Deferred tax assets, tax credit research and development derecognized amount	0
State
Income Tax Examination [Line Items]
Net operating loss carryforwards	68,200,000	33,200,000
State | Research and Development Credit Carry Forwards
Income Tax Examination [Line Items]
Research and development credit carryforwards	5,600,000	5,100,000
Federal
Income Tax Examination [Line Items]
Net operating loss carryforwards	76,000,000	41,100,000
Net operating loss carryforwards, valuation allowance	221,700,000
Deferred tax assets, net operating loss carryforwards derecognized amount	46,600,000
Deferred tax assets, tax credit research and development derecognized amount	5,100,000
Federal | Research and Development Credit Carry Forwards
Income Tax Examination [Line Items]
Research and development credit carryforwards	$ 1,600,000	$ 600,000