Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share	4,688,252	1,224,199
Common stock subject to repurchase [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share	45,000	45,000
Warrants to purchase common stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share	3,323,876	118,881
Common stock options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share	1,275,624	1,037,500
Employee stock purchase plan [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share	43,752	22,818