Stockholder's Equity - Summary of Stock Options Activity (Detail) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares
Number of Shares
Number of Shares, Beginning balance | shares	1,515,923
Number of Shares, Options granted | shares	483,328
Number of Shares, Options cancelled | shares	(97,382)
Number of Shares, Options exercised | shares	(2,000)
Number of Shares, Ending balance | shares	1,899,869
Number of Shares, Outstanding and expected to vest | shares	1,870,009
Number of Shares, Exercisable | shares	1,490,943
Weighted Average Exercise Price
Weighted Average Exercise Price, Beginning balance | $ / shares	$ 18.65
Weighted Average Exercise Price, Options granted | $ / shares	5.55
Weighted Average Exercise Price, Options cancelled | $ / shares	96.15
Weighted Average Exercise Price, Options exercised | $ / shares	0.66
Weighted Average Exercise Price, Ending balance | $ / shares	11.35
Weighted Average Exercise Price, Outstanding and expected to vest | $ / shares	11.41
Weighted Average Exercise Price, Exercisable | $ / shares	$ 12.01
Weighted Average Remaining Contractual Life (in years)
Weighted Average Remaining Contractual Life (in years)	7 years
Weighted Average Remaining Contractual Life, Outstanding and expected to vest	6 years 10 months 24 days
Weighted Average Remaining Contractual Life, Exercisable	6 years 3 months 18 days
Aggregate Intrinsic Value, Options outstanding | $	$ 9,294
Aggregate Intrinsic Value, Outstanding and expected to vest | $	9,244
Aggregate Intrinsic Value, Exercisable | $	$ 8,612