Loss Per Share - Summary of Potentially Dilutive Common Stock Equivalents (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Average unamortized share-based compensation expense:
Exercise prices on common stock options, lower range	$ 3.00	$ 3.00	$ 3.00	$ 3.00
Exercise prices on common stock options, upper range	10.00	10.00	10.00	10.00
Weighted average exercise price of the Warrants	$ 5.64	$ 5.64	$ 5.64	$ 5.64
Restricted Common Stock Awards
Average unamortized share-based compensation expense:
Average unamortized share-based compensation expense	$ 3.0	$ 2.5	$ 3.3	$ 2.6
Restricted Stock Unit Awards
Average unamortized share-based compensation expense:
Average unamortized share-based compensation expense	$ 0.9	$ 1.3	$ 0.9	$ 1.8