Summary of Stock Options Outstanding (Detail)	12 Months Ended
Dec. 31, 2018 $ / shares shares
Number of Shares
Outstanding at January 1, 2018 \| shares	7,089,440
Granted \| shares	5,158,648
Exercised \| shares	(6,880)
Forfeited \| shares	(733,536)
Expired \| shares	(531,554)
Outstanding at December 31, 2018 \| shares	10,976,118
Exercisable at December 31, 2018 \| shares	3,672,480
Weighted Average Exercise Price per Share
Outstanding at January 1, 2018 \| $ / shares	$ 9.33
Granted \| $ / shares	1.94
Exercised \| $ / shares	1.10
Forfeited \| $ / shares	2.87
Expired \| $ / shares	20.56
Outstanding at December 31, 2018 \| $ / shares	5.75
Exercisable at December 31, 2018 \| $ / shares	$ 13.03

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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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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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.

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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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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

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