Equity Financing - Additional Information (Detail) - USD ($)							1 Months Ended			12 Months Ended
	Jan. 07, 2021	Jan. 04, 2021	Dec. 06, 2019	Dec. 03, 2019	Aug. 17, 2018	Aug. 14, 2018	Feb. 28, 2018	Jan. 31, 2017	Sep. 30, 2016	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 31, 2019	Apr. 19, 2018	Apr. 30, 2017
Subsidiary Sale Of Stock [Line Items]
Proceed from private placement and equity issuances, gross								$ 26,100,000	$ 13,800,000
Preferred stock conversion rate														100.00%
Underwriters | Common Stock
Subsidiary Sale Of Stock [Line Items]
Underwriting agreement date				Dec. 03, 2019		Aug. 14, 2018
Number of shares issued in transaction				41,550,000		16,216,217
Sale of stock, price				$ 3.13		$ 9.25
Option to purchase additional shares				30 days		30 days
Aggregate proceeds from issuance of common stock			$ 138,400,000		$ 161,900,000
Underwriters | Common Stock | Subsequent Event
Subsidiary Sale Of Stock [Line Items]
Underwriting agreement date		Jan. 04, 2021
Number of shares issued in transaction		11,856,500
Sale of stock, price		$ 4.85
Aggregate proceeds from issuance of common stock	$ 53,500,000
Underwriters | Common Stock | Maximum
Subsidiary Sale Of Stock [Line Items]
Number of additional shares issued in transaction				6,232,500		2,432,432
March 2018 Direct Registered Offering
Subsidiary Sale Of Stock [Line Items]
Proceed from private placement and equity issuances, gross							$ 59,100,000
March 2018 Direct Registered Offering | Common Stock
Subsidiary Sale Of Stock [Line Items]
Stock issued during period							4,090,000
March 2018 Direct Registered Offering | Series A Convertible Preferred Stock
Subsidiary Sale Of Stock [Line Items]
Stock issued during period							3,000,581
March 2018 Direct Registered Offering Warrants
Subsidiary Sale Of Stock [Line Items]
Warrants to purchase common stock, shares							1,418,116
Warrant exercise price							$ 8.31
Warrant expiration date							2025-03
At The Market Offering Program January and April 2017 | Maximum
Subsidiary Sale Of Stock [Line Items]
Maximum common stock saleable shares, value															$ 50,000,000.0
At The Market Offering Program January and April 2017 | Common Stock
Subsidiary Sale Of Stock [Line Items]
Aggregate proceeds from issuance of common stock												$ 300,000
Stock issued during period												33,097
Average market price per share												$ 8.41
At The Market Offering Program January 2019 | Maximum
Subsidiary Sale Of Stock [Line Items]
Maximum common stock saleable shares, value													$ 100,000,000.0
Maximum aggregate offering price													$ 250,000,000.0
At The Market Offering Program January 2019 | Common Stock
Subsidiary Sale Of Stock [Line Items]
Stock issued during period										0	0
At The Market Offering Program January 2021 | Subsequent Event
Subsidiary Sale Of Stock [Line Items]
Maximum common stock saleable shares, value	$ 42,900,000