Stockholders' Equity - Additional Information (Detail) - USD ($) shares in Millions		12 Months Ended
	Jan. 08, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stockholders Equity Note [Line Items]
Net proceeds from public offering		$ 26,931,000	$ 85,036,000	$ 30,197,000
Cantor Fitzgerald & Co | Amendment No. 3 | Sales Agreement
Stockholders Equity Note [Line Items]
Maximum common stock offering price	$ 70,000,000.0
Percentage of proceeds payable as compensation to underwriter	2.00%
Unsold shares of common stock, value	$ 31,400,000
Common stock, number of shares issued		5.6	4.2
Net proceeds from public offering		$ 26,900,000	$ 27,900,000
Common stock registered for sale		$ 14,100,000