Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended				3 Months Ended			9 Months Ended		12 Months Ended
	Aug. 31, 2019	Sep. 30, 2016	Aug. 31, 2015	Jul. 31, 2015	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018	Jan. 31, 2017	Dec. 31, 2013
Common Stock Warrants [Line Items]
Placement warrants not exercised and remained outstanding					2,156,153			2,156,153
(Gain) loss related to change in fair value								$ (1,281)	$ (4,674)
2018 Direct Registered Offering | Common Stock
Common Stock Warrants [Line Items]
Warrants issued							1,418,116
Exercise price							$ 8.31
Common stock warrants, expiration date							Mar. 31, 2025
Proceed from private placement and equity issuances, gross							$ 59,100
Fair value of warrants upon issuance							7,400
Allocated portion of proceeds from issuance of stock and warrants							$ 6,600
2013 Placement Warrants
Common Stock Warrants [Line Items]
Warrants issued												128,231
Exercise price												$ 5.84
Common stock warrants, expiration date								Dec. 16, 2023
Number of warrant exercised	128,231
Stock issued during period	36,457
Placement warrants not exercised and remained outstanding					0			0
2015 Placement Warrants
Common Stock Warrants [Line Items]
Warrants issued			198,760	198,760
Exercise price			$ 5.00	$ 5.00
Number of warrant exercised										159,010
Stock issued during period										92,487
Placement warrants not exercised and remained outstanding					0			0
Warrant expiration period			5 years	5 years
Number of warrant expired			39,750	39,750
2016 Placement Warrants
Common Stock Warrants [Line Items]
Warrants issued		1,380,745
Exercise price		$ 2.95			$ 2.95			$ 2.95
Placement warrants not exercised and remained outstanding					537,263			537,263
Warrant expiration period		7 years						7 years
2017 Placement Warrants
Common Stock Warrants [Line Items]
Warrants issued											1,720,512
Exercise price					$ 3.17			$ 3.17			$ 3.17
Placement warrants not exercised and remained outstanding					1,618,890			1,618,890
Warrant expiration period								7 years
2016 and 2017 Private Placement Warrants | Common Stock
Common Stock Warrants [Line Items]
(Gain) loss related to change in fair value					$ 2,000	$ (13,500)		$ (1,300)	$ (8,600)