Income Taxes - Income Tax Reconciliation (Detail)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
Expected income tax benefit at the federal statutory rate	21.00%	34.00%	34.00%
State taxes, net of federal benefit	0.00%	0.00%	0.00%
Change in federal statutory rate	0.00%	(54.10%)	0.00%
Non-deductible items and other	(0.20%)	0.50%	(0.70%)
Federal and state credits	0.70%	0.50%	0.60%
Change in valuation allowance	(21.50%)	19.10%	(33.90%)
Total	0.00%	0.00%	0.00%

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
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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 the difference, between reported income tax expense (benefit) and the expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations, that is attributable to tax exempt income, equity in earnings (loss) of an unconsolidated subsidiary, minority interest income (expense), tax holiday, disposition of a business, disposition of an asset, repatriation of foreign earnings, repatriation of foreign earnings jobs creation act of 2004, change in enacted tax rate, prior year income taxes, change in deferred tax asset valuation allowance, and other adjustments.

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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 applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Effective income tax rate reconciliation nondeductible expense and other.

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Effective income tax rate reconciliation tax credits adjustment.

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