Changes in Fair Value of Common Stock Warrant Liability (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Warrants And Rights Note Disclosure [Abstract]
Common stock warrant liability, beginning balance	$ 6.9	$ 5.6
Change in fair value of common stock warrant liability	0.6	(0.7)
Common stock warrant liability, ending balance	$ 7.5	$ 4.9