Stockholders' Equity - Additional Information (Detail) - USD ($)			1 Months Ended	12 Months Ended
	Dec. 11, 2020	Jan. 08, 2018	Jan. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stockholders Equity Note [Line Items]
Common stock, shares issued and sold				168,170,000	144,291,000
Common stock, par value				$ 0.001	$ 0.001
Net proceeds from public offering				$ 76,534,000	$ 26,931,000	$ 85,036,000
Common Stock
Stockholders Equity Note [Line Items]
Common stock, number of shares issued				19,338,000	5,648,000	18,202,000
Underwritten Public Offering | Common Stock
Stockholders Equity Note [Line Items]
Common stock, shares issued and sold			16,866,667
Common stock, par value			$ 0.001
Common stock, sale of stock, price per share			$ 3.75
Net proceeds from public offering			$ 62,700,000
Amendment No. 3 | Cantor Fitzgerald & Co | Sales Agreements
Stockholders Equity Note [Line Items]
Net proceeds from public offering				$ 13,900,000
Percentage of proceeds payable as compensation to underwriter		2.00%
Common stock, number of shares issued				2,500,000
Amendment No. 3 | Cantor Fitzgerald & Co. and Stifel, Nicolaus & Company, Incorporated | Sales Agreements
Stockholders Equity Note [Line Items]
Percentage of proceeds payable as compensation to underwriter	2.00%
Common stock, number of shares issued				0
Maximum common stock offering price	$ 100,000,000.0