Common Stock Warrants - Summary of Outstanding Warrants to Purchase Shares of Common Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2021	Mar. 23, 2021	Dec. 31, 2020	Nov. 29, 2019	Apr. 16, 2019
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	11,249,128		13,354,403
Class Of Warrant Or Right. Aggregate Proceeds From Warrants Issued		$ 435		$ 21,000
Class of Warrant or Right, Additional Exercise Price of Warrants or Rights		$ 0.01		$ 0.001
Funded
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)		8.69
Pre Funded Warrant
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)				11.999	$ 10.999
Class B Warrants
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)		$ 8.70		15.00
Class A Warrant
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)					$ 13.20
Issuance On October 25, 2016
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 19.78
Issuance On October 25, 2016 | Legacy Warrants
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	5,155
Issuance On December 28, 2017 One
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 19.78
Issuance On December 28, 2017 One | Legacy Warrants
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	115,916
Issuance On September 12, 2018 One
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 19.78
Issuance On September 12, 2018 One | Legacy Warrants
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	20,220
Issuance On October 19, 2018
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 19.78
Issuance On October 19, 2018 | Legacy Warrants
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	20,016
Issuance On March 13, 2019
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 19.78
Issuance On March 13, 2019 | Legacy Warrants
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	5,000
Issuance On April 16, 2019
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 13.20
Issuance On April 16, 2019 | Class A Warrant
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	3,866,154
Issuance On November 29, 2019
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 8.70
Issuance On November 29, 2019 | Class B Warrants
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	5,416,667
Issuance On November 29, 2019 One
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 12.00
Issuance On November 29, 2019 One | Pre Funded Warrant
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	1,750,000
Issuance On March 23, 2021
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 8.70
Issuance On March 23, 2021 | Pre Funded Warrant
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	50,000
Pre Funded Warrant
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)				$ 11.999