Assets and Liabilities Measured at Fair Value on Recurring Basis Based on Fair Value Hierarchy (Detail) - USD ($) $ in Millions	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	$ 0.0		$ 0.6
Derivative liabilities as classified in the unaudited condensed consolidated balance sheet	(0.2)		(0.4)
Common stock warrant liability, estimated fair value	(2.1)	$ (1.9)	(4.4)	$ (6.1)	$ (7.5)	$ (6.9)
Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Net derivative assets (liabilities)	(0.2)		0.2
Fair Value, Recurring | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	0.0		0.6
Derivative liabilities as classified in the unaudited condensed consolidated balance sheet	(0.2)		(0.4)
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	$ (2.1)		$ (4.4)