Income Taxes (Reconciliation of the Federal Statutory and Effective Income Tax Rate) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Disclosure [Abstract]
Income before income taxes	$ 58.0	$ 112.3	$ 62.7
Statutory taxes at 35.0%	20.3	39.3	21.9
State income taxes	1.6	1.9	1.2
Non-deductible expenses	1.1	1.3	1.2
Unremitted foreign earnings	0.1	0.1	0
Foreign statutory rate differences	(0.3)	(1.2)	(0.4)
Valuation allowance	0	0	0.1
Percentage depletion	(5.0)	(6.9)	(7.2)
R&D and other federal credits	(0.1)	(0.2)	(0.1)
Tax controversy resolution	(0.4)	(0.1)	(1.1)
Domestic production deduction	(0.7)	0	0
Other	(0.8)	(1.4)	0
Income tax provision	15.8	32.8	15.6
Effective income tax rate	27.20%	29.20%	24.90%
Cumulative unremitted earnings of foreign subsidiaries	9.0
Cumulative deferred tax liabilities of unremitted foreign earnings	$ 0.1	$ 0.1