Stock-Based Compensation - Summary of Stock Option Activity (Detail)	9 Months Ended
	Sep. 30, 2019 $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Issuable Under Options, Beginning balance | shares	4,435,000
Shares Issuable Under Options, Granted | shares	999,000
Shares Issuable Under Options, Exercised | shares	(45,882)
Shares Issuable Under Options, Cancelled | shares	(522,000)
Shares Issuable Under Options, Ending balance | shares	4,865,658
Shares Issuable Under Options, Options vested and expected to vest at June 30, 2019 | shares	4,866,000
Shares Issuable Under Options, Options exercisable at June 30, 2019 | shares	2,905,000
Weighted Average Exercise Price Per Share, Beginning balance | $ / shares	$ 19.21
Weighted Average Exercise Price Per Share, Granted | $ / shares	13.45
Weighted Average Exercise Price Per Share, Exercised | $ / shares	0.19
Weighted Average Exercise Price Per Share, Cancelled | $ / shares	20.25
Weighted Average Exercise Price Per Share, Ending balance | $ / shares	18.10
Weighted Average Exercise Price Per Share, Options vested and expected to vest at June 30, 2019 | $ / shares	18.10
Weighted Average Exercise Price Per Share, Options exercisable at June 30, 2019 | $ / shares	$ 18.32