Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Income tax provision	$ 0	$ 0
Statutory income tax rate	21.00%	21.00%
Unrecognized tax benefits that would have tax impact	$ 0
Unrecognized tax benefits, interest and penalties accrued	0
Unrecognized tax benefits position will significantly change over the next twelve months	0
Net valuation allowance, increased (decreased)	4,100,000
Unrecognized tax benefit	1,865,000	$ 1,847,000	$ 1,812,000
Domestic tax authority [Member]
Income Taxes [Line Items]
Net operating loss carry-forwards	475,800,000
Research and development tax credit carry-forwards	$ 9,700,000
Net operating loss carry-forwards expiration	2021
State and local jurisdiction [Member]
Income Taxes [Line Items]
Net operating loss carry-forwards	$ 335,000,000
Research and development tax credit carry-forwards	$ 8,900,000
Net operating loss carry-forwards expiration	2028