Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [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		$ 618,000	$ 23,758,000
Tax benefit on exercise of non-qualified stock options and disqualified disposition of incentive stock options		840,000
Unrecognized tax benefits, related interest and penalties		$ 0	$ 0
Tax examinations, description		Tax years 2006 through 2017 remain open to U.S. federal and state tax examinations.
Income tax rate		34.00%	34.00%	34.00%
Reduction in deferred tax assets		$ 25,913,000
Maximum [Member]
Income Taxes [Line Items]
Income tax rate		35.00%
Scenario Plan [Member]
Income Taxes [Line Items]
Income tax rate	21.00%
Earliest Tax Year [Member]
Income Taxes [Line Items]
Open tax years		2006
Latest Tax Year [Member]
Income Taxes [Line Items]
Open tax years		2017
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 205,135,000
Federal [Member] | R&D Tax Credit Carryforwards [Member]
Income Taxes [Line Items]
Tax credit carryforwards		$ 7,378,000
Federal [Member] | Earliest Tax Year [Member]
Income Taxes [Line Items]
Tax loss carryforwards expiration year		2026
Federal [Member] | Earliest Tax Year [Member] | R&D Tax Credit Carryforwards [Member]
Income Taxes [Line Items]
Tax credit expiration year		2025
State and Local [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 198,350,000
State and Local [Member] | R&D Tax Credit Carryforwards [Member]
Income Taxes [Line Items]
Tax credit carryforwards		$ 1,033,000
State and Local [Member] | Earliest Tax Year [Member]
Income Taxes [Line Items]
Tax loss carryforwards expiration year		2027