Outstanding Stock Options and Stock Awards Excluded from Calculation of Net Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock Options and Stock Awards
Outstanding securities not included in diluted net loss per share calculation (in thousands):
Outstanding securities not included in diluted net loss per share calculation	9,789	7,344	5,981
Warrants
Outstanding securities not included in diluted net loss per share calculation (in thousands):
Outstanding securities not included in diluted net loss per share calculation	5,841
Series B Convertible Preferred Stock
Outstanding securities not included in diluted net loss per share calculation (in thousands):
Outstanding securities not included in diluted net loss per share calculation	4,840