Number of new stock issued during the period.

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Stockholders' Equity - Additional Information (Detail) - USD ($) shares in Millions		9 Months Ended
	Jan. 08, 2018	Sep. 30, 2019	Sep. 30, 2018
Stockholders Equity Note [Line Items]
Net proceeds from public offering		$ 17,803,000	$ 79,301,000
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		3.5
Net proceeds from public offering		$ 17,700,000
Common stock registered for sale		$ 23,500,000