Warrants - Outstanding Warrants To Purchase Common Stock Warrants (Detail) - Common Stock	9 Months Ended
	Sep. 30, 2021 $ / shares shares
Class of Warrant or Right [Line Items]
Number of shares underlying warrants (in shares)	3,132
Original issue date of April 2016
Class of Warrant or Right [Line Items]
Exercise price (in dollars per share) | $ / shares	$ 1.12
Number of shares underlying warrants (in shares)	3,132
Original issue date of April 2016 | Original Term
Class of Warrant or Right [Line Items]
Original Term	7 years