Stock-Based Compensation - Schedule of Information Related to Stock Options Outstanding (Detail) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Stock Options, Outstanding	60,618
Number of Stock Options, Granted	339,619
Number of Stock Options, Exercised	(9,541)
Number of Stock Options, Forfeited or expired	(37,422)
Number of Stock Options, Outstanding	353,274	60,618
Number of Stock Options, Exercisable	15,278
Number of Stock Options, Expected to vest	337,996
Weighted-average Exercise Price, Outstanding	$ 128.23
Weighted-average Exercise Price, Granted	4.63
Weighted-average Exercise Price, Exercised	2.40
Weighted-average Exercise Price, Forfeited or expired	145.58
Weighted-average Exercise Price, Outstanding	10.97	$ 128.23
Weighted-average Exercise Price, Exercisable	106.08
Weighted-average Exercise Price, Expected to vest	$ 6.67
Weighted-average Remaining Contractual Term, Outstanding	6 years 14 days	4 years 5 months 12 days
Weighted-average Remaining Contractual Term, Exercisable	5 years 3 months 14 days
Weighted-average Remaining Contractual Term, Expected to vest	6 years 25 days

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of share options (or share units) exercised during the current period.

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