Summary of Series B Convertible Preferred Stock and Accretion of Dividend (Detail) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Stockholders Equity [Line Items]
Cumulative dividends on Series B convertible preferred stock	$ 275	$ 262	$ 818	$ 780
Series B convertible preferred stock
Stockholders Equity [Line Items]
Balance as of December 31, 2019			21,875
Cumulative dividends on Series B convertible preferred stock			818
Balance as of September 30, 2020	$ 22,693		$ 22,693
Balance as of December 31, 2019, Shares			5,469
Cumulative dividends on Series B convertible preferred stock			204
Balance as of June 30, 2020, Shares	5,673		5,673