Common Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions				1 Months Ended
	Jul. 17, 2018	Nov. 14, 2017	Nov. 06, 2017	Nov. 30, 2017
Underwritten Public Offering [Member]
Class Of Stock [Line Items]
Net proceeds from issuance of common stock	$ 70.5
Offering expenses payable	$ 1.0
Series A Convertible Preferred Stock [Member] | Underwritten Public Offering [Member]
Class Of Stock [Line Items]
Issuance of stock, shares	2,220
Share price	$ 12,500
Common Stock [Member]
Class Of Stock [Line Items]
Net proceeds from issuance of common stock		$ 6.1	$ 71.6	$ 74.2
Common Stock [Member] | Underwritten Public Offering [Member]
Class Of Stock [Line Items]
Issuance of stock, shares	3,780,000
Share price	$ 12.50