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	$ 26,756	$ 21,512	$ 13,955
Percentage of provision for income taxes at U.S. statutory rates	35.00%	35.00%	35.00%
Increase (decrease) in taxes resulting from:
Percentage depletion	(4,900)	(3,870)	(3,257)
Percent of pretax income, Percentage depletion	(6.30%)	(6.40%)	(8.20%)
State taxes, net of federal benefit	2,154	1,547	731
Percent of pretax income, State taxes, net of federal benefit	2.80%	2.50%	1.80%
Foreign tax rates	(2,123)	(1,226)	(4,560)
Percent of pretax income, Foreign tax rates	(2.80%)	(2.00%)	(11.40%)
Change in reserve for tax uncertainties	(364)		(2,975)
Percent of pretax income, Change in reserve for tax uncertainties	(0.50%)	0.00%	(7.50%)
Audit settlement	(118)		2,083
Percent of pretax income, Audit settlement	(0.20%)	0.00%	5.20%
Discrete items related to foreign tax filings	1,393
Percent of pretax income, Discrete items related to foreign tax filings	1.80%	0.00%	0.00%
Foreign tax credits	(2,359)	(2,178)	(880)
Percent of pretax income, Foreign tax credits	(3.00%)	(3.50%)	(2.20%)
Changes to valuation allowance	(517)	2,591	28
Percent of pretax income, Changes to valuation allowance	(0.70%)	4.20%	0.10%
Tax from foreign disregarded entities	262	1,414	142
Percent of pretax income, Tax from foreign disregarded entities	0.30%	2.30%	0.40%
Other	1,665	(399)	68
Percent of pretax income, Other	2.20%	(0.60%)	0.20%
Income Tax Expense (Benefit), Continuing Operations, Total	$ 21,849	$ 19,391	$ 5,335
Percent of pretax income, Effective tax rates related to income from continuing operations before income taxes	28.60%	31.50%	13.40%