Income Taxes - Reconciliation of Federal Statutory Income Tax Rate and Effective Income Tax Rate (Detail)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory rate	21.00%	34.00%
Change in valuation allowance	(1.00%)
Warrant liability FMV adjustment	1.00%	(8.00%)
Research and development credits	4.00%	3.00%
Removal of net operating loss and other credits	(22.00%)	33.00%
Impact of federal tax rate change		(65.00%)
Stock compensation and other permanent items	(3.00%)	3.00%

Effective income tax rate reconciliation deductible expense share based compensation and other permanent items.

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- Definition

Effective income tax rate reconciliation fair market value of warrant liability adjustment.

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- Definition

Effective income tax rate reconciliation operating loss and tax credits other.

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Effective income tax rate reconciliation tax credits research and development.

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

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I)
-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

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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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I)
-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

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-Section 50
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-SubTopic 10
-Section 50
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