Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019
Fair Value Assumptions Expected volatility Rate Maximum	78.85%	81.66%
Fair Value Assumptions Risk Free Interest Rate Maximum	2.42%	2.91%
Fair Value Assumptions Expected Term1		6 years
Fair Value Assumptions Expected Dividend Rate	0.00%	0.00%
Securities Purchase Agreement [Member]
Gross proceeds received			$ 47.1
Private Placement [Member]
Number of securities into which the class of warrant converted	18,939,394		18,939,394
Warrant Exercise Per share	$ 3.01		$ 3.01
fair value of adjustment of warrants			$ 18.4
Fair Value Assumptions Expected volatility Rate Maximum			71.00%
Fair Value Assumptions Risk Free Interest Rate Maximum			2.99%
Fair Value Assumptions Expected Term1			5 years
Fair Value Assumptions Expected Dividend Rate			0.00%

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

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Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

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Amount of expense (income) related to adjustment to fair value of warrant liability.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

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