Income Taxes - Reconciliation of Federal Statutory Income Tax Rate (Detail)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory income (benefit) tax rate	21.00%	21.00%	34.00%
2017 Tax Act, net deferred tax remeasurement	0.00%	0.00%	626.73%
State taxes, net of federal benefit	(0.18%)	(0.11%)	2.01%
Stock compensation	(5.39%)	(4.74%)	5.18%
Permanent differences-other	(7.67%)	(1.33%)	13.39%
North Carolina tax rate change	0.00%	0.00%	32.75%
Research and development (“R&D”) credit	0.00%	0.00%	(5.54%)
Valuation release for bargain purchase gain	0.00%	0.00%	302.23%
Other	1.71%	(2.07%)	1.36%
Decrease (increase) in valuation allowance	(9.44%)	(12.65%)	(709.88%)
Effective tax rate	0.03%	0.10%	302.23%

Effective income tax rate reconciliation bargain purchase gain valuation percent.

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Effective income tax rate reconciliation permanent differences.

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Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act, Percent

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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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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to nondeductible expense for share-based payment arrangement.

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