Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Taxes
Income tax expense (benefit)	$ 0.0	$ (0.5)	$ 1.9	$ 0.4
U.S.
Income Taxes
Net operating loss carry forwards	$ 913.5		$ 913.5		$ 913.5
Net operating loss expiration period					20 years
Net operating loss carry forwards expiration year					Dec. 31, 2027
Non-U.S.
Income Taxes
Net operating loss carry forwards					$ 30.6