Income Taxes - Reconciliation of Statutory Federal Income Tax Rate to Effective Income Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income taxes computed at statutory rates	$ 6,832	$ 6,892
(Increases) decreases resulting from:
State income taxes, net of federal tax benefit	451	143
Federal and state research and experimentation credits	947	781
Change in valuation allowance	(7,830)	(7,873)
Impact of expired tax positions	0	0
Impact of recent U.S. tax reform	0	0
Other	(401)	36
Total tax benefit (provision)	$ (1)	$ (21)
Income taxes computed at statutory rates, Percentage	(21.00%)	(21.00%)
(Increases) decreases resulting from:
State income taxes, net of federal tax benefit, Percentage	(1.00%)	(1.00%)
Federal and state research and experimentation credits, Percentage	(3.00%)	(2.00%)
Change in valuation allowance, Percentage	24.00%	24.00%
Impact of expired tax positions, Percentage	0.00%	0.00%
Impact of recent U.S. tax reform, Percentage	0.00%	0.00%
Other, Percentage	1.00%	0.00%
Total, Percentage	0.00%	0.00%

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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