Unaudited Quarterly Financial Information - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effect Of Fourth Quarter Events [Line Items]
Property, plant and equipment, net	$ 289.2				$ 301.5				$ 289.2	$ 301.5
Deferred income taxes (liability)	2.5				6.7				2.5	6.7
Net earnings (loss)									(102.6)	(6.8)	$ 5.4
Cost of sales	293.3	$ 298.3	$ 298.6	$ 292.8	277.1	$ 313.2	$ 347.4	$ 133.0	1,183.0	1,070.7	0.0
Selling, general and administrative expenses									$ 61.0	56.0	10.0
Immaterial error correction									Management has concluded that the error reflected in the December 31, 2015 consolidated financial statements was not material and that the error correction in 2016 is not material to the full year results of operations.
Goodwill impairment	$ 61.8								$ 61.8	0.0	$ 0.0
Pretax gain on sale of NABCO								$ 39.7
Recovery of the repurchase reserve							$ 4.3
Overstatement Due To Depreciation Expense Error
Effect Of Fourth Quarter Events [Line Items]
Property, plant and equipment, net					3.8					3.8
Deferred income taxes (liability)					$ 1.1					1.1
Net earnings (loss)										$ 2.7
Adjustment To Correct Depreciation Expense Error
Effect Of Fourth Quarter Events [Line Items]
Cost of sales									3.7
Selling, general and administrative expenses									$ 0.1