Income Taxes (Summary of the Total Deferred Tax Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets
Tax carryforwards	$ 7.0	$ 12.4
Inventories	3.1	4.0
Accrued expenses and reserves	24.0	23.3
Accrued pension benefits	7.4	9.9
Other employee benefits	8.0	5.8
Other	7.2	7.0
Total deferred tax assets	56.7	62.4
Less: Valuation allowance	3.1	3.0
Deferred tax assets, net of valuation allowance	53.6	59.4
Deferred tax liabilities
Depreciation and depletion	45.0	35.8
Partnership investment - development costs	19.9	18.7
Unremitted foreign earnings	0.1	0.1
Total deferred tax liabilities	65.0	54.6
Net deferred tax asset (liability)	$ (11.4)	$ 4.8