Income Tax Matters - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred income tax assets:
Loss and credit carryforwards	$ 39.6	$ 47.7
Defined benefit plans	3.6	2.9
Other assets	36.8	36.3
Lease assets	8.7	10.6
Inventories	29.5	46.9
Excess interest carryforward	14.0	12.2
Research & development capitalization	16.9	8.7
Valuation allowances	(2.7)	(3.7)
Total deferred income tax assets	146.4	161.6
Deferred income tax liabilities:
Property, plant and equipment	(142.6)	(147.0)
Lease liabilities	(8.7)	(9.3)
Undistributed foreign earnings	(3.0)	(2.7)
Total deferred income tax liabilities	(154.3)	(159.0)
Net deferred income tax assets		$ 2.6
Net deferred income tax liabilities	$ (7.9)