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]
Corporate income tax rate		34.00%	34.00%
Valuation allowance, deferred tax asset, (decrease) increase		$ (13,414,000)	$ 17,312,000
Operating loss carryforwards, federal		127,132,000
Operating loss carryforwards, state		83,428,000
Unrecognized tax benefits		535,000	488,000	$ 333,000
Scenario, Forecast [Member]
Income Taxes [Line Items]
Corporate income tax rate	21.00%
Federal [Member]
Income Taxes [Line Items]
Provision for income taxes		$ 0	0
Operating loss carryforwards, expiration year		2037
Tax credit carryforwards, research and development		$ 5,171,000
State [Member]
Income Taxes [Line Items]
Provision for income taxes		$ 0	$ 0
Operating loss carryforwards, expiration year		2037
Tax credit carryforwards, research and development		$ 819,000