Stockholders' Equity - Additional Information (Detail) - Cantor Fitzgerald & Co - Amendment No. 3 - Sales Agreement - USD ($)		3 Months Ended
Jan. 08, 2018	Mar. 31, 2019
Stockholders Equity Note [Line Items]
Maximum common stock offering price	$ 70,000,000
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		0
Common stock registered for sale		$ 41,600,000

Number of new stock issued during the period.

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