Income Taxes (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Effective Income Tax Rate Reconciliation
Provision for income taxes at U.S. statutory rates	$ 26,337	[1]	$ 21,234	[1]	$ 12,962	[1]
Percentage of provision for income taxes at U.S. statutory rates (in hundredths)	35.00%	[1]	35.00%	[1]	35.00%	[1]
Increase (decrease) in taxes resulting from:
Percentage depletion	(4,900)	[1]	(3,870)	[1]	(3,257)	[1]
Percent of pretax income, Percentage depletion (in hundredths)	(6.50%)	[1]	(6.40%)	[1]	(8.80%)	[1]
State taxes, net of federal benefit	2,185	[1]	1,546	[1]	754	[1]
Percent of pretax income, State taxes, net of federal benefit (in hundredths)	2.90%	[1]	2.60%	[1]	2.00%	[1]
Foreign tax rates	(1,045)	[1]	(924)	[1]	(4,356)	[1]
Percent of pretax income, Foreign tax rates (in hundredths)	(1.40%)	[1]	(1.50%)	[1]	(11.70%)	[1]
Change in reserve for tax uncertainties	(710)	[1]	64	[1]	(2,741)	[1]
Percent of pretax income, Change in reserve for tax uncertainties (in hundredths)	(0.90%)	[1]	0.10%	[1]	(7.40%)	[1]
Audit settlement	(118)	[1]	0	[1]	2,083	[1]
Percent of pretax income, Audit settlement (in hundredths)	(0.10%)	[1]	0.00%	[1]	5.60%	[1]
Discrete items related to foreign tax filings	(210)	[1]	178	[1]	0	[1]
Percent of pretax income, Discrete items related to foreign tax filings (in hundredths)	(0.30%)	[1]	0.30%	[1]	0.00%	[1]
Foreign tax credits	(2,359)	[1]	(2,178)	[1]	(879)	[1]
Percent of pretax income, Foreign tax credits (in hundredths)	(3.10%)	[1]	(3.60%)	[1]	(2.40%)	[1]
Changes to valuation allowance	(216)	[1]	3,354	[1]	28	[1]
Percent of pretax income, Changes to valuation allowance (in hundredths)	(0.30%)	[1]	5.60%	[1]	0.10%	[1]
Tax from foreign disregarded entities	262	[1]	1,358	[1]	142	[1]
Percent of pretax income, Tax from foreign disregarded entities (in hundredths)	0.30%	[1]	2.20%	[1]	0.40%	[1]
Other	1,560	[1]	(460)	[1]	627	[1]
Percent of pretax income, Other (in hundredths)	2.00%	[1]	(0.80%)	[1]	1.70%	[1]
Income Tax Expense (Benefit), Continuing Operations, Total	$ 20,786	[1]	$ 20,302	[1]	$ 5,363	[1]
Percent of pretax income, Effective tax rates related to income from continuing operations before income taxes (in hundredths)	27.60%	[1]	33.50%	[1]	14.50%	[1]

[1] Restated