Stock-Based Compensation - Summary of Option Activity (Detail) - 2006 Plan and 2016 Plan - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Number of Shares
Beginning balance (in shares)	4,495,145
Granted (in shares)	627,500
Forfeited (in shares)	(225,000)
Expired (in shares)	(557,604)
Exercised (in shares)	(568,973)
Ending balance (in shares)	3,771,068	4,495,145
Exercisable at end of period (in shares)	2,639,153
Vested and expected to vest at end of period (in shares)	3,604,062
Weighted Average Exercise Price at Grant Date
Beginning balance (in dollars per share)	$ 12.21
Granted (in dollars per share)	11.27
Forfeited (in dollars per share)	18.83
Expired (in dollars per share)	14.21
Exercised (in dollars per share)	7.39
Ending balance (in dollars per share)	12.09	$ 12.21
Exercisable at end of period (in dollars per share)	11.17
Vested and expected to vest at end of period (in dollars per share)	$ 12.05
Weighted Average Remaining Term (Years)
Weighted Average Remaining Term	5 years 9 months 7 days	5 years 6 months 29 days
Exercisable at end of period	4 years 5 months 1 day
Vested and expected to vest at end of period	5 years 7 months 9 days
Aggregate Intrinsic Value
Beginning balance	$ 22,148
Exercised	2,155
Ending balance	3,331	$ 22,148
Exercisable at end of period	3,331
Vested and expected to vest at end of period	$ 3,331