Equity Incentive Plans - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares Outstanding, Beginning Balance	944	1,115	1,328
Number of Shares, Exercised	(10)	(49)	(177)
Number of Shares, Forfeited or cancelled	(50)	(122)	(36)
Number of Shares Outstanding, Ending Balance	884	944	1,115
Number of Shares, Vested and Exercisable	884
Weighted-Average Exercise Price, Beginning Balance	$ 2.20	$ 2.45	$ 2.50
Weighted-Average Exercise Price, Exercised	1.92	1.75	2.42
Weighted-Average Exercise Price, Forfeited or cancelled	2.87	4.65	4.40
Weighted-Average Exercise Price, Ending Balance	2.17	$ 2.20	$ 2.45
Weighted-Average Exercise Price, Vested and Exercisable	$ 2.17
Weighted-Average Remaining Contractual Life (Years)	1 year 9 months 10 days
Weighted-Average Remaining Contractual Life (Years), Vested and Exercisable	1 year 9 months 10 days
Aggregate Intrinsic Value Outstanding, Beginning Balance	$ 627	$ 970	$ 6,175
Aggregate Intrinsic Value, Exercised	11	70	407
Aggregate Intrinsic Value Outstanding, Ending Balance	722	$ 627	$ 970
Aggregate Intrinsic Value, Vested and Exercisable	$ 722