Stockholders' Equity, Accumulated Other Comprehensive Income (Loss) and Noncontrolling Interest - Change in Stockholders' Equity (Deficit) (Detail) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Beginning Balance	$ 293.5	$ 174.7	$ 145.1	$ 163.7	$ 185.4	$ 178.6	$ 145.1	$ 178.6
Beginning Balance, shares			38,329,897				38,329,897
Beginning Balance Treasury Stock, shares			212,500				212,500
Net income (loss)	50.0	113.3	$ 25.6	(39.7)	(25.5)	16.4	$ 188.9	(48.8)
Foreign currency translation	(3.5)	1.6		1.2	1.6	(8.5)
Changes in defined benefit pension and other post-retirement benefit plans, net of tax	90.7	2.0	2.0	5.8	2.0	1.8
Share repurchases	(0.9)
Stock-based compensation expense	1.2	1.5	1.6	0.4	0.4	0.6
Cash dividends	(3.1)
Interest rate swap, net of tax	0.4	0.4	0.4
Cash flow hedge - interest rate swap, net of tax				0.3		(3.5)
Dividends paid to non-controlling interest					(0.2)			(0.2)
Ending Balance	$ 428.3	293.5	174.7	131.7	163.7	185.4	$ 428.3	131.7
Ending Balance, shares	38,687,094						38,687,094
Ending Balance Treasury Stock, shares	251,427						251,427
Common Stock [Member]
Beginning Balance	$ 0.4	$ 0.4	$ 0.4	$ 0.4	$ 0.4	$ 0.4	$ 0.4	$ 0.4
Beginning Balance, shares	38,687,000	38,330,000	38,330,000	38,330,000	37,996,000	37,996,000	38,330,000	37,996,000
Stock-based compensation expense, shares		357,000			334,000
Ending Balance	$ 0.4	$ 0.4	$ 0.4	$ 0.4	$ 0.4	$ 0.4	$ 0.4	$ 0.4
Ending Balance, shares	38,687,000	38,687,000	38,330,000	38,330,000	38,330,000	37,996,000	38,687,000	38,330,000
Treasury Stock [Member]
Beginning Balance	$ (6.6)	$ (6.6)	$ (6.6)	$ (6.6)	$ (6.6)	$ (6.6)	$ (6.6)	$ (6.6)
Beginning Balance Treasury Stock, shares	213,000	213,000	213,000	213,000	213,000	213,000	213,000	213,000
Share repurchases	$ (0.9)
Shares repurchases treasury stock, Shares	38,000
Ending Balance	$ (7.5)	$ (6.6)	$ (6.6)	$ (6.6)	$ (6.6)	$ (6.6)	$ (7.5)	$ (6.6)
Ending Balance Treasury Stock, shares	251,000	213,000	213,000	213,000	213,000	213,000	251,000	213,000
Capital in Excess of Par Value [Member]
Beginning Balance	$ 386.2	$ 384.7	$ 383.1	$ 382.2	$ 381.8	$ 381.2	$ 383.1	$ 381.2
Stock-based compensation expense	1.2	1.5	1.6	0.4	0.4	0.6
Ending Balance	387.4	386.2	384.7	382.6	382.2	381.8	387.4	382.6
Retained Earnings (Accumulated Deficit) [Member]
Beginning Balance	172.0	59.1	33.8	90.4	116.0	99.6	33.8	99.6
Net income (loss)	49.7	112.9	25.3	(39.9)	(25.6)	16.4
Cash dividends	(3.1)
Ending Balance	218.6	172.0	59.1	50.5	90.4	116.0	218.6	50.5
Foreign Currency Translation [Member]
Beginning Balance	(45.4)	(46.9)	(47.0)	(55.4)	(57.1)	(48.6)	(47.0)	(48.6)
Foreign currency translation	(3.4)	1.5	0.1	1.2	1.7	(8.5)
Ending Balance	(48.8)	(45.4)	(46.9)	(54.2)	(55.4)	(57.1)	(48.8)	(54.2)
Benefit Plan Liabilities [Member]
Beginning Balance	(217.8)	(219.8)	(221.8)	(249.3)	(251.3)	(253.1)	(221.8)	(253.1)
Changes in defined benefit pension and other post-retirement benefit plans, net of tax	90.7	2.0	2.0	5.8	2.0	1.8
Ending Balance	(127.1)	(217.8)	(219.8)	(243.5)	(249.3)	(251.3)	(127.1)	(243.5)
Interest Rate Swap [Member]
Beginning Balance	(2.3)	(2.7)	(3.1)				(3.1)
Interest rate swap, net of tax	0.4	0.4	0.4
Ending Balance	(1.9)	(2.3)	(2.7)				(1.9)
Cash Flow Hedge - Interest Rate Swap [Member]
Beginning Balance				(3.8)	(3.8)	(0.3)		(0.3)
Cash flow hedge - interest rate swap, net of tax				0.3		(3.5)
Ending Balance				(3.5)	(3.8)	(3.8)		(3.5)
Non-controlling Interest [Member]
Beginning Balance	7.0	6.5	6.3	5.8	6.0	6.0	6.3	6.0
Net income (loss)	0.3	0.4	0.3	0.2	0.1
Foreign currency translation	(0.1)	0.1	(0.1)		(0.1)
Dividends paid to non-controlling interest					(0.2)
Ending Balance	$ 7.2	$ 7.0	$ 6.5	$ 6.0	$ 5.8	$ 6.0	$ 7.2	$ 6.0