Share-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Shares Available for Grant
Options outstanding, beginning balance (in shares)	699,376	1,023,378
Additional shares reserved under plan (in shares)		0
Options granted (in shares)	(633,030)	(626,757)
Options forfeited (in shares)	322,117	302,755
Options outstanding, ending balance (in shares)	388,463	699,376
Shares Subject to Outstanding Options
Options outstanding, beginning balance (in shares)	1,671,666	1,399,484
Options granted (in shares)	658,030	727,257
Options forfeited (in shares)	(507,950)	(403,748)
Options exercised (in shares)	(32,443)	(51,327)
Options outstanding, ending balance (in shares)	1,789,303	1,671,666
Vested and expected to vest (in shares)	1,731,437	1,585,689
Exercisable (in shares)	1,032,801	1,007,870
Weighted-Average Exercise Price Per Share
Options outstanding, beginning balance (in USD per share)	$ 5.42	$ 7.17
Options granted (in USD per share)	2.36	2.97
Options forfeited (in USD per share)	7.07	7.61
Options exercised (in USD per share)	2.12	1.16
Options outstanding, ending balance (in USD per share)	3.89	5.42
Vested and expected (in USD per share)	3.94	5.53
Exercisable (in USD per share)	$ 4.81	$ 6.58
Weighted- Average Remaining Contractual Term (in years)
Options outstanding	8 years 11 days
Vested and expected	7 years 11 months 27 days	8 years 1 month 10 days
Exercisable	7 years 2 months 12 days	7 years 6 months 15 days
Aggregate Intrinsic Value
Options outstanding	$ 638
Vested and expected to vest	597	$ 2
Exercisable	$ 190	$ 2