Exercise price per share or per unit of warrants or rights outstanding.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(i)(4))
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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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Value of input used to measure outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
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Period between issuance and expiration of outstanding warrant and right embodying unconditional obligation requiring redemption by transferring asset at specified or determinable date or upon event certain to occur, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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Summary of Significant Accounting Policies - Schedule of Fair Value Determined Using Black-Scholes Model (Detail)	Dec. 31, 2018 $ / shares	Dec. 31, 2017	Aug. 16, 2017	Mar. 09, 2017 $ / shares
Class Of Warrant Or Right [Line Items]
Warrants exercise price per share	$ 5.03			$ 0.01
Expected Volatility [Member] \| Common Stock Warrants [Member]
Class Of Warrant Or Right [Line Items]
Fair value of warrants	93.90	91.30	86.90	84.40
Expected Volatility [Member] \| Common Stock Warrants [Member] \| Pre-trigger Fair Value [Member]
Class Of Warrant Or Right [Line Items]
Fair value of warrants	82.50
Expected Volatility [Member] \| Common Stock Warrants [Member] \| Post-trigger Fair Value [Member]
Class Of Warrant Or Right [Line Items]
Fair value of warrants	82.50
Expected Term (Years) [Member] \| Common Stock Warrants [Member]
Class Of Warrant Or Right [Line Items]
Fair value of warrants, expected term (years)	3 years 7 months 6 days	4 years 7 months 6 days	5 years	5 years
Expected Term (Years) [Member] \| Common Stock Warrants [Member] \| Pre-trigger Fair Value [Member]
Class Of Warrant Or Right [Line Items]
Fair value of warrants, expected term (years)	4 years 11 months 23 days
Expected Term (Years) [Member] \| Common Stock Warrants [Member] \| Post-trigger Fair Value [Member]
Class Of Warrant Or Right [Line Items]
Fair value of warrants, expected term (years)	4 years 11 months 23 days
Risk-free Interest Rate [Member] \| Common Stock Warrants [Member]
Class Of Warrant Or Right [Line Items]
Fair value of warrants	2.48	2.16	1.76	2.13
Risk-free Interest Rate [Member] \| Common Stock Warrants [Member] \| Pre-trigger Fair Value [Member]
Class Of Warrant Or Right [Line Items]
Fair value of warrants	3.07
Risk-free Interest Rate [Member] \| Common Stock Warrants [Member] \| Post-trigger Fair Value [Member]
Class Of Warrant Or Right [Line Items]
Fair value of warrants	3.07
Stock Price [Member] \| Common Stock Warrants [Member] \| Pre-trigger Fair Value [Member]
Class Of Warrant Or Right [Line Items]
Warrants exercise price per share	$ 4.94
Stock Price [Member] \| Common Stock Warrants [Member] \| Post-trigger Fair Value [Member]
Class Of Warrant Or Right [Line Items]
Warrants exercise price per share	4.94
Exercise Price [Member] \| Common Stock Warrants [Member] \| Pre-trigger Fair Value [Member]
Class Of Warrant Or Right [Line Items]
Warrants exercise price per share	6.00
Exercise Price [Member] \| Common Stock Warrants [Member] \| Post-trigger Fair Value [Member]
Class Of Warrant Or Right [Line Items]
Warrants exercise price per share	$ 4.18