Stock-Based Compensation - Summary of Assumptions Used in Black-Scholes Option Pricing Model (Detail)		12 Months Ended
Jan. 01, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum		1.55%	2.51%	1.85%
Risk-free interest rate, maximum		2.62%	3.09%	2.57%
Expected volatility, minimum		71.10%	82.60%	75.30%
Expected volatility, maximum		75.20%	92.80%	84.50%
Expected dividend yield		0.00%	0.00%	0.00%
Re-Measurement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield		0.00%	0.00%	0.00%
Share-based Payment Arrangement, Nonemployee [Member] \| Consultants [Member] \| Re-Measurement [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate, minimum	2.59%		1.82%	1.28%
Risk-free interest rate, maximum	2.62%		3.02%	2.39%
Expected volatility, minimum	58.90%		58.20%	74.60%
Expected volatility, maximum	84.60%		101.00%	87.30%
Share-based Payment Arrangement, Nonemployee [Member] \| Consultants [Member] \| Re-Measurement [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)	9 months 22 days		3 months	7 months 13 days
Share-based Payment Arrangement, Nonemployee [Member] \| Consultants [Member] \| Re-Measurement [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)	8 years 2 months 9 days		8 years 11 months 9 days	9 years 11 months 9 days
Employee Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility			75.00%	79.00%
Expected volatility, minimum		71.00%	83.00%	75.00%
Expected volatility, maximum		75.00%	93.00%	85.00%
Expected dividend yield		0.00%
Expected life of options (in years)		6 years 3 months
Employee Options [Member] \| Share-based Payment Arrangement, Nonemployee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)				10 years
Employee and Board of Directors Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life of options (in years)		6 years 3 months	6 years 3 months	6 years 3 months

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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- Definition

The estimated measure of the 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.

+ References

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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.

+ References

No definition available.

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The estimated measure of the minimum 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.

+ References

No definition available.

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- Definition

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

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No definition available.

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- Definition

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

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No definition available.

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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.

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No definition available.

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
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-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

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