Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Benefit [Line Items]
Net operating loss carryforwards, federal	$ 229,900,000
Net operating loss carryforwards, state	$ 236,800,000
Net operating loss carryforwards, begins to expiring year	2034
Net operating loss carryforwards, expiration date description	begins to expire in 2034
Research and development and other credit	$ 19,417,000	$ 11,766,000
Research and development tax credits, expiration date description	begin to expire in 2035 and 2031
Increase in valuation allowance	$ 34,500,000	$ 28,700,000	$ 14,800,000
Unrecognized tax benefits	0
Operating Loss Carryforward Indefinitely [Member]
Income Tax Benefit [Line Items]
Net operating loss carryforwards, federal	193,000,000.0
Operating Loss Carryforward Indefinitely Begins to Expire in 2034 [Member]
Income Tax Benefit [Line Items]
Net operating loss carryforwards, federal	36,900,000
Federal [Member]
Income Tax Benefit [Line Items]
Research and development and other credit	$ 12,600,000
Research and development tax credits, expiration year	2035
State [Member]
Income Tax Benefit [Line Items]
Research and development and other credit	$ 8,700,000
Research and development tax credits, expiration year	2031