Consolidated Statements of Stockholder's Equity Consolidated Statements of Stockholder's Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2020		16,572
Beginning balance at Dec. 31, 2020	$ 521.1	$ 0.0	$ 16.6	$ 558.8	$ (54.3)
Net income	12.1			12.1
Stock-based compensation expense	2.0		2.0
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		105
Stock-based compensation expense	(1.1)		(1.1)
Pension and other postretirement employee benefit plans, net of tax	1.9				1.9
Ending balance (in shares) at Mar. 31, 2021		16,678
Ending balance at Mar. 31, 2021	536.1	$ 0.0	17.6	570.9	(52.4)
Beginning balance (in shares) at Dec. 31, 2020		16,572
Beginning balance at Dec. 31, 2020	521.1	$ 0.0	16.6	558.8	(54.3)
Net income	(39.6)
Ending balance (in shares) at Jun. 30, 2021		16,685
Ending balance at Jun. 30, 2021	488.1	$ 0.0	19.3	519.2	(50.5)
Beginning balance (in shares) at Mar. 31, 2021		16,678
Beginning balance at Mar. 31, 2021	536.1	$ 0.0	17.6	570.9	(52.4)
Net income	(51.6)			(51.6)
Stock-based compensation expense	1.9		1.9
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		7
Stock-based compensation expense	(0.1)		(0.1)
Pension and other postretirement employee benefit plans, net of tax	1.9				1.9
Ending balance (in shares) at Jun. 30, 2021		16,685
Ending balance at Jun. 30, 2021	488.1	$ 0.0	19.3	519.2	(50.5)
Beginning balance (in shares) at Dec. 31, 2021		16,692
Beginning balance at Dec. 31, 2021	511.7	$ 0.0	23.6	530.7	(42.6)
Net income	16.6			16.6
Stock-based compensation expense	2.0		2.0
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		119
Stock-based compensation expense	(1.5)		(1.5)
Pension and other postretirement employee benefit plans, net of tax	1.1				1.1
Ending balance (in shares) at Mar. 31, 2022		16,811
Ending balance at Mar. 31, 2022	530.0	$ 0.0	24.1	547.3	(41.4)
Beginning balance (in shares) at Dec. 31, 2021		16,692
Beginning balance at Dec. 31, 2021	511.7	$ 0.0	23.6	530.7	(42.6)
Net income	31.3
Ending balance (in shares) at Jun. 30, 2022		16,770
Ending balance at Jun. 30, 2022	544.7	$ 0.0	23.0	562.0	(40.3)
Beginning balance (in shares) at Mar. 31, 2022		16,811
Beginning balance at Mar. 31, 2022	530.0	$ 0.0	24.1	547.3	(41.4)
Net income	14.7			14.7
Stock-based compensation expense	3.8		3.8
Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture		78
Stock-based compensation expense	(1.0)		(1.0)
Pension and other postretirement employee benefit plans, net of tax	$ 1.1				1.1
Stock Repurchased and Retired During Period, Shares	(119)
Stock Repurchased and Retired During Period, Value	$ (3.9)		(3.9)
Ending balance (in shares) at Jun. 30, 2022		16,770
Ending balance at Jun. 30, 2022	$ 544.7	$ 0.0	$ 23.0	$ 562.0	$ (40.3)