Warrant Liabilities - Fair Value of Convertible Preferred Stock Warrant Liability (Detail)	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Series C Warrant [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Volatility	90.00%	90.00%
Expected Term	1 year 11 months 1 day	2 years 2 months 1 day
Expected dividend yield	0.00%	0.00%
Risk-free rate	2.26%	1.91%
2017 PIPE Warrant Liability [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Volatility	62.00%	67.00%
Expected Term	9 months 18 days	9 months 18 days
Expected dividend yield	0.00%	0.00%
Risk-free rate	2.09%	1.76%

Expected dividends to be paid to holders of the underlying shares or financial instruments (expressed as a percentage of the share or instrument's price).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

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Risk-free interest rate assumption used in valuing an instrument.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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