Unaudited Quarterly Financial Information - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended								9 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effect Of Fourth Quarter Events
Property, plant and equipment, net	$ 247.5				$ 289.2					$ 247.5	$ 289.2
Net earnings (loss)									$ (58.0)	(120.8)	(102.6)	$ (6.8)
Cost of sales	311.0	$ 320.5	$ 332.1	$ 323.7	293.3	$ 298.3	$ 298.6	$ 292.8		1,287.3	1,183.0	1,070.7
Selling, general and administrative expenses										52.3	61.0	56.0
Goodwill impairment		$ 33.6			$ 61.8					33.6	61.8	0.0
Impairment on intangible assets	10.1									10.1	0.1	0.0
Property, plant and equipment impairment	40.5									40.5
Reorganization items, net	11.7									11.7
Provisional income tax benefit resulting from the Tax Cuts and Jobs Act of 2017	$ 8.9									$ (8.9)
Overstatement Due To Depreciation Expense Error
Effect Of Fourth Quarter Events
Property, plant and equipment, net												3.8
Deferred income taxes (liability)												1.1
Net earnings (loss)												$ 2.7
Adjustment To Correct Depreciation Expense Error
Effect Of Fourth Quarter Events
Cost of sales											3.7
Selling, general and administrative expenses											$ 0.1