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Summary of Option Activity Under Company's Equity Incentive Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares Underlying Outstanding Options
Number of Shares Underlying Outstanding Options, Beginning Balance	1,577,541	1,361,977
Number of Shares Underlying Outstanding Options, Options granted	1,091,250	450,900
Number of Shares Underlying Outstanding Options, Options exercised	(44,605)	(41,219)
Number of Shares Underlying Outstanding Options, Options forfeited	(250,641)	(182,722)
Number of Shares Underlying Outstanding Options, Options expired	(17,930)	(11,395)
Number of Shares Underlying Outstanding Options, Ending Balance	2,355,615	1,577,541	1,361,977
Number of Shares Underlying Outstanding Options, Exercisable- December 31, 2020	1,113,791
Shares available to be granted - December 31, 2020	1,255,302
Weighted- Average Exercise Price
Weighted- Average Exercise Price, Beginning Balance	$ 10.85	$ 12.04
Weighted- Average Exercise Price, Options granted	6.26	7.85
Weighted- Average Exercise Price, Options exercised	5.04	4.57
Weighted- Average Exercise Price, Options forfeited	10.32	8.36
Weighted- Average Exercise Price, Options expired	51.12	96.49
Weighted- Average Exercise Price, Ending Balance	8.59	$ 10.85	$ 12.04
Weighted- Average Exercise Price, Exercisable - December 31, 2020	$ 10.45
Weighted-Average Remaining Contractual Term (Years)
Weighted-Average Remaining Contractual Term (Years), Outstanding Balance	7 years 11 months 15 days	8 years 1 month 24 days	8 years 8 months 15 days
Weighted Average Remaining Contractual Term, Exercisable - December 31, 2020	7 years 1 month 20 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Outstanding	$ 1,350	$ 2,294
Aggregate Intrinsic Value, Options exercised	116	159
Aggregate Intrinsic Value, Outstanding	1,337	$ 1,350	$ 2,294
Aggregate Intrinsic Value, Exercisable - December 31, 2020	$ 823

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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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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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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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