Financings - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	May 11, 2017	Feb. 17, 2015	Feb. 09, 2015	Feb. 03, 2015
Class of Stock [Line Items]
Stock issued during period	9,708,738
Issuance & sale of common stock in public offering price per share	$ 5.15
Sale of stock price per share	$ 4.893
Net proceeds from issuance of common stock	$ 47.3
J.P. Morgan Securities Inc.
Class of Stock [Line Items]
Stock issued during period		1,500,000	10,000,000	10,000,000
Issuance & sale of common stock in public offering price per share				$ 8.75
Option granted, exercisable period				30 days
Sale of stock price per share				$ 8.225
Net proceeds from issuance of common stock		$ 94.3