Preferred and Common Stock Warrants - Summary of Outstanding Warrants to Purchase Shares of Common Stock (Detail) - $ / shares	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	13,506,040	13,656,871	6,490,204	5,146,400
Issuance On October 25, 2016
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	5,155
Exercise Price (usd per share)	$ 19.78
Issuance On November 1, 2017
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	130,609
Exercise Price (usd per share)	$ 19.78
Issuance On November 17, 2017
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	8,442
Exercise Price (usd per share)	$ 19.78
Issuance On December 4, 2017
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	5,661
Exercise Price (usd per share)	$ 19.78
Issuance On December 28, 2017
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	6,925
Exercise Price (usd per share)	$ 19.78
Issuance On December 28, 2017 One
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	115,916
Exercise Price (usd per share)	$ 19.78
Issuance On September 12, 2018
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	25,275
Exercise Price (usd per share)	$ 19.78
Issuance On September 12, 2018 One
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	20,220
Exercise Price (usd per share)	$ 19.78
Issuance On October 19, 2018
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	20,016
Exercise Price (usd per share)	$ 19.78
Issuance On March 13, 2019
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	5,000
Exercise Price (usd per share)	$ 19.80
Issuance On April 16, 2019
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	3,866,154
Exercise Price (usd per share)	$ 13.20
Issuance On April 16, 2019 One
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	2,130,000
Exercise Price (usd per share)	$ 11.00
Issuance On November 29, 2019
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	5,416,667
Exercise Price (usd per share)	$ 15.00
Issuance On November 29, 2019 One
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	1,750,000
Exercise Price (usd per share)	$ 12.00