Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes
Unrecognized tax benefits	$ 0.3		$ 0.3	$ 0.1	$ 0.3
Effect of Tax Cuts and Jobs Act of 2017
U.S. federal statutory rate			34.00%	34.00%	34.00%
Decrease in U.S. valuation allowance due to reduced corporate tax rate under Tax Cuts and Jobs Act of 2017			$ 140.9
Provisional income tax benefit resulting from the Tax Cuts and Jobs Act of 2017	(8.9)		8.9
U.S.
Income Taxes
Deferred tax valuation allowance			249.5	$ 400.6
Net operating loss carry forwards	960.5		$ 960.5
Net operating loss carry forwards expiration year			Dec. 31, 2017
Net operating loss expiration period			20 years
Foreign
Income Taxes
Deferred tax valuation allowance			$ 6.6	$ 5.4
Net operating loss carry forwards	29.5		29.5
State
Income Taxes
Net operating loss carry forwards	$ 337.4		$ 337.4
Maximum
Effect of Tax Cuts and Jobs Act of 2017
U.S. federal statutory rate			35.00%
Forecast
Effect of Tax Cuts and Jobs Act of 2017
U.S. federal statutory rate		21.00%