Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
Sep. 12, 2019	Mar. 31, 2020	Mar. 31, 2019
Fair Value Assumptions Expected volatility Rate Maximum		73.01%	85.00%
Fair Value Assumptions Risk Free Interest Rate Maximum		1.68%	2.53%
Fair Value Assumptions Expected Dividend Rate		0.00%	0.00%
Net Proceeds from Underwriting		$ 13,015
Proceeds from private placement	$ 52,500
MD Anderson Warrant [Member]
Number of securities into which the class of warrant converted		3,333,333
Warrant Exercise Per share		$ 0.001
fair value of adjustment of warrants		$ 14,500
Warrant Expiry date		Dec. 31, 2026
Securities Purchase Agreement [Member]
Net Proceeds from Underwriting		$ 47,100
Private Placement [Member]
Number of securities into which the class of warrant converted	17,803,031	18,939,394
Warrant Exercise Per share	$ 3.01	$ 3.01
fair value of adjustment of warrants		$ 18,400
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%
Placement agent fees and other expenses	$ 1,100
Private Placement [Member] \| New Warrants [Member]
Number of securities into which the class of warrant converted	17,803,031
Warrant Exercise Per share	$ 7.00
Non-cash inducement warrant expense		$ 60,800

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 cash inflow associated with the amount received from entity's raising of capital via private rather than public placement.

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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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Expiration date 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 CCYY-MM-DD format.

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Non Operating Income Expense Inducement Of Warrants.

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Placement agent fees and other related expenses.

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