Common Stock Reserved for Issuance - Schedule of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Total shares of common stock reserved	22,967,741	21,576,339
Shares available for future stock option grants
Class Of Stock [Line Items]
Total shares of common stock reserved	948,415	1,908,626
ESPP shares available for issuance
Class Of Stock [Line Items]
Total shares of common stock reserved	2,743,340	1,780,020
Warrants to purchase common stock
Class Of Stock [Line Items]
Total shares of common stock reserved	3,614,019	4,426,244
Options To Purchase Common Stock
Class Of Stock [Line Items]
Total shares of common stock reserved	11,165,846	11,603,708
Shares issuable upon settlement of restricted stock units outstanding
Class Of Stock [Line Items]
Total shares of common stock reserved	4,496,121	1,857,741