Subsequent Events - Additional Information (Detail) - Common Stock [Member] - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Apr. 30, 2019	Apr. 30, 2018
Subsequent Event [Line Items]
Total shares issued		14,200,000
Public offering price of common stock issued		$ 16.25
Net proceeds from issuance of common stock, after deducting offering expenses		$ 215.8
Subsequent Event [Member]
Subsequent Event [Line Items]
Total shares issued	12,650,000
Public offering price of common stock issued	$ 11.50
Net proceeds from issuance of common stock, after deducting offering expenses	$ 136.2
Subsequent Event [Member] | Underwriters [Member]
Subsequent Event [Line Items]
Total shares issued	1,650,000