Shareholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
	Jul. 12, 2018	Mar. 31, 2019	Dec. 31, 2018	Apr. 28, 2017
Class of Warrant or Right [Line Items]
Common stock, par value		$ 0.001	$ 0.001
Common and preferred stock, shares authorized		201,000,000
Common stock, shares authorized		200,000,000	200,000,000
Preferred stock, shares authorized		1,000,000
Preferred stock, par value		$ 0.001
H.C. Wainwright & Co., LLC [Member]
Class of Warrant or Right [Line Items]
Common stock, par value				$ 0.001
Sales commissions in fixed percentage of gross proceeds per share				3.00%
Common stock, shares sold		647,426
Net proceeds from sale of shares		$ 4.9
H.C. Wainwright & Co., LLC [Member] | Common Stock [Member]
Class of Warrant or Right [Line Items]
Value of shares sold prior to amendment	$ 2.3
H.C. Wainwright & Co., LLC [Member] | Maximum [Member]
Class of Warrant or Right [Line Items]
Amount available to sell under equity program				$ 60.0