Assets and Liabilities Measured at Fair Value on Recurring Basis Based on Fair Value Hierarchy (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Common stock warrant liability, estimated fair value	$ (6.9)	$ (5.6)	$ (9.3)	$ (2.4)
Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net derivative liabilities	(0.7)
Fair Value, Recurring | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	0.2
Derivative liabilities	(0.9)
Fair Value, Recurring | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Common stock warrant liability, estimated fair value	$ (6.9)	$ (5.6)