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Common Stock and Warrants - Fair Value of Warrants Estimated Using Black-Scholes Option Pricing Model with Weighted Average Assumptions (Detail) |  |  |  | 3 Months Ended |
--- | --- | --- | --- | --- | ---
Dec. 29, 2017 $ / shares | Dec. 28, 2017 $ / shares | Dec. 22, 2017 $ / shares | Mar. 31, 2018 $ / shares | Mar. 31, 2017 $ / shares | Mar. 31, 2018 $ / shares
Warrants Granted |  |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |  |  |  |  |
Stock price |  |  |  |  |  | $ 5.45
Exercise price |  |  |  |  |  | $ 7.50
Warrant term |  |  |  | 3 years |  |
Expected volatility |  |  |  | 83.83% |  |
Risk-free interest rate |  |  |  | 0.60% |  |
Dividend rate |  |  |  | 0.00% |  |
Warrants Granted | December 2017 Financing |  |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |  |  |  |  |
Stock price | $ 12.32 | $ 12.45 | $ 10.60 |  |  |
Exercise price | $ 12.25 | $ 12.25 | $ 12.25 |  |  |
Warrant term | 3 years | 3 years | 3 years |  |  |
Expected volatility | 60.24% | 60.24% | 60.24% |  |  |
Risk-free interest rate | 1.98% | 2.00% | 2.01% |  |  |
Dividend rate | 0.00% | 0.00% | 0.00% |  |  |
Warrants Outstanding |  |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items] |  |  |  |  |  |
Stock price |  |  |  | $ 10.11 | $ 7.80 |
Exercise price |  |  |  | $ 12.72 | $ 8.10 |
Warrant term |  |  |  | 2 years 3 months 14 days | 1 year 7 months 24 days |
Expected volatility |  |  |  | 63.77% | 94.21% |
Risk-free interest rate |  |  |  | 2.26% | 0.75% |
Dividend rate |  |  |  | 0.00% | 0.00% |

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- Definition 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. + References No definition available. + Details
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- Definition Agreed upon price for the exchange of the underlying asset. + 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 + Details
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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 + Details
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