Stockholders' Equity - Additional Information (Detail) - USD ($) shares in Millions		6 Months Ended
	Jan. 08, 2018	Jun. 30, 2019	Jun. 30, 2018
Stockholders Equity Note [Line Items]
Net proceeds from public offering		$ 6,783,000	$ 69,117,000
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		2.0
Net proceeds from public offering		$ 9,800,000
Common stock registered for sale		$ 31,500,000