Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax [Line Items]
Tax provision or benefit			$ 0	$ 0	$ 0
Net operating loss carryforwards	$ 300,000		$ 300,000
Corporate federal tax rate			34.00%	34.00%	34.00%
Reduction of deferred tax assets	34,500,000
Limit of utilization of net operating losses (NOLs) and tax credits description			Under the rules, such an ownership change is generally any change in ownership of more than 50% of a company’s stock within a rolling three-year period. The rules generally operate by focusing on changes in ownership among stockholders considered by the rules as owning, directly or indirectly, 5% or more of the stock of a company and any change in ownership arising from new issuances of stock by the company.
Liabilities for unrecognized tax benefits	0		$ 0	$ 0
Maximum [Member]
Income Tax [Line Items]
Corporate federal tax rate			35.00%
Scenario, Plan [Member]
Income Tax [Line Items]
Corporate federal tax rate		21.00%
Federal [Member]
Income Tax [Line Items]
Net operating loss carryforwards	190,100,000		$ 190,100,000
Operating loss carryforwards expiration year			2029
Federal [Member] | Research and Development Tax Credit Carryforwards [Member]
Income Tax [Line Items]
Tax credit carryforwards	5,400,000		$ 5,400,000
Tax credit expiration year			2029
State and Local Jurisdiction [Member]
Income Tax [Line Items]
Net operating loss carryforwards	147,800,000		$ 147,800,000
Operating loss carryforwards expiration year			2030
State and Local Jurisdiction [Member] | Research and Development Tax Credit Carryforwards [Member]
Income Tax [Line Items]
Tax credit carryforwards	$ 2,900,000		$ 2,900,000
Tax credit expiration year			2025