Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Percentage of annual research and development credit for cash	65.00%
Valuation allowance on the deferred tax asset	100.00%	100.00%
Change in valuation allowance	$ 24,321,000	$ 23,642,000
Unrecognized tax benefits, related interest and penalties	$ 0	$ 0
Tax examinations, description	tax years 2006 through 2019 remain open to U.S. federal and state tax examinations.
Income taxes using U.S. federal statutory rate	21.00%	21.00%	34.00%
Maximum [Member]
Operating Loss Carryforwards [Line Items]
Income taxes using U.S. federal statutory rate			35.00%
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 349,525,000
Operating Loss Carryforwards, Limitations on Use	80%
Federal [Member] | R&D Tax Credit Carryforwards [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 15,274,000
Federal [Member] | Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards expiration year	2026
Federal [Member] | Earliest Tax Year [Member] | R&D Tax Credit Carryforwards [Member]
Operating Loss Carryforwards [Line Items]
Tax credit expiration year	2025
State and Local [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 189,157,000
State and Local [Member] | R&D Tax Credit Carryforwards [Member]
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 1,448,000
State and Local [Member] | Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Tax loss carryforwards expiration year	2027