Share-Based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares
Shares Subject to Outstanding Options
Options outstanding (in shares) | shares	1,671,666
Options granted (in shares) | shares	658,030
Options forfeited (in shares) | shares	(384,695)
Options exercised (in shares) | shares	(12,999)
Options outstanding (in shares) | shares	1,932,002
Weighted-Average Exercise Price Per Share
Options outstanding (in USD per share) | $ / shares	$ 5.42
Options granted (in USD per share) | $ / shares	2.36
Options forfeited (in USD per share) | $ / shares	7.26
Options exercised (in USD per share) | $ / shares	0.76
Options outstanding (in USD per share) | $ / shares	$ 4.05
Weighted- Average Remaining Contractual Term (in years)
Options outstanding	8 years 2 months 27 days
Aggregate Intrinsic Value
Options outstanding | $	$ 211