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Fair Value Measurements - Summary of Common Stock Warrant Liability and Derivative Liability Valuation Assumptions (Detail) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Private Placement Common Stock Warrant Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock Price	$ 7.97	$ 7.34
Exercise Price	$ 1.12	$ 1.12
Remaining term (in years)	5 years 14 days	5 years 3 months 14 days
Volatility	68.00%	66.00%
Risk-free interest rate	2.53%	2.21%
Placement Agent Common Stock Warrant Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock Price	$ 7.97	$ 7.34
Exercise Price	$ 1.12	$ 1.12
Remaining term (in years)	3 years 14 days	3 years 3 months 14 days
Volatility	84.00%	82.00%
Risk-free interest rate	2.37%	1.99%
JGB Common Stock Warrant Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock Price	$ 0	$ 7.34
Exercise Price	$ 0	$ 4.67
Remaining term (in years)	0 years	4 years 8 months 15 days
Volatility	0.00%	69.00%
Risk-free interest rate	0.00%	1.89%
Majority Shareholder Common Stock Warrant Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock Price	$ 7.97	$ 7.34
Exercise Price	$ 4.00	$ 4.00
Remaining term (in years)	5 years 2 months 15 days	5 years 5 months 15 days
Volatility	67.00%	65.00%
Risk-free interest rate	2.54%	2.21%
Derivative Liability [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Stock Price	$ 7.79	$ 7.34
Remaining term (in years)	14 days	2 years 1 month 28 days
Volatility	45.00%	69.00%
Risk-free interest rate	1.70%	2.14%

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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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Agreed upon price for the exchange of the underlying asset.

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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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- Definition

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.

+ References

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

+ References

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

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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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Price of a single share of a number of saleable stocks of a company.

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