Summary of Significant Accounting Policies - Schedule of Outstanding Common Stock Equivalents Excluded From Computations of Diluted Net Loss per Common Share (Detail) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock excluded from computation of diluted net loss per share (in shares)	2,040,266	1,385,842
Warrants to Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock excluded from computation of diluted net loss per share (in shares)	274,524	199,524
Options to Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock excluded from computation of diluted net loss per share (in shares)	1,765,742	1,186,318