Income Taxes - Reconciliation of Federal Statutory Income Tax Rate and Effective Income Tax Rate (Detail)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal statutory rate	34.00%	34.00%
Warrant liability FMV adjustment	(8.00%)	6.00%
Stock issuance costs		(5.00%)
Research and development credits	3.00%	3.00%
Removal of net operating loss and other credits	33.00%	(33.00%)
Impact of federal tax rate change	(65.00%)
Stock compensation and other permanent items	3.00%	(5.00%)

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.

+ References

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- Definition

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

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- Definition

Effective income tax rate reconciliation stock issuance costs.

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- Definition

Effective income tax rate reconciliation tax credits research and development.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-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

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319

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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 income tax rates.

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