Stock-Based Compensation and Employee Stock Purchase Program - Summary of Activity Under Stock Incentive Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Subject to Outstanding, Beginning Balance	661,701	530,044
Shares Subject to Outstanding, Options granted	502,494	208,571
Shares Subject to Outstanding, Options exercised		(546)
Shares Subject to Outstanding, Options Forfeited	(174,508)	(30,132)
Shares Subject to Outstanding, Options Expired	(99,928)	(46,236)
Shares Subject to Outstanding, Ending Balance	889,759	661,701
Shares Subject to Outstanding, Vested and expected to vest	841,991
Shares Subject to Outstanding, Exercisable	502,973
Weighted-Average Exercise Price Per Share, Outstanding Beginning Balance	$ 21.60	$ 35.53
Weighted-Average Exercise Price Per Share, Options granted	4.28	5.13
Weighted-Average Exercise Price Per Share, Options exercised		4.63
Weighted-Average Exercise Price Per Share, Options forfeited	5.91	33.95
Weighted-Average Exercise Price Per Share, Options expired	25.56	98.69
Weighted Average Exercise Price Per Share, Outstanding Ending Balance	14.46	$ 21.60
Weighted Average Exercise Price Per Share, Vested and expected to vest	15.03
Weighted Average Exercise Price Per Share, Exercisable	$ 22.20
Aggregate Intrinsic Value, Outstanding Balance	$ 240	$ 305
Aggregate Intrinsic Value, Vested and expected to vest	$ 240

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

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