Common Stock Reserved for Issuance - Schedule of Common Stock Reserved for Issuance (Detail) - shares	Dec. 31, 2020	Dec. 31, 2019	Jul. 15, 2015
Class of Stock [Line Items]
Total common stock reserved for future issuance	16,386,314	18,577,117
Series A Warrant [Member]
Class of Stock [Line Items]
Total common stock reserved for future issuance	7,802,241	7,802,241
Series B Warrant [Member]
Class of Stock [Line Items]
Total common stock reserved for future issuance	2,574,727	2,574,727
Equity Incentive Plans [Member]
Class of Stock [Line Items]
Total common stock reserved for future issuance	1,117,796	51,514
Awards outstanding	4,146,928	326,023
2015 Employee Stock Purchase Plan [Member]
Class of Stock [Line Items]
Total common stock reserved for future issuance	17,500	17,500	17,500
Warrants to Purchase Common Stock [Member]
Class of Stock [Line Items]
Outstanding warrants	727,122	1,839
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Total common stock reserved for future issuance		7,803,273