Income Taxes (Details 2)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of the federal statutory and effective income tax rate
Federal statutory rate	35.00%	35.00%	35.00%
State and local income taxes, net of federal tax effect	0.80%	(0.80%)	(0.30%)
Effect of excess of percentage depletion over cost depletion	(5.10%)	(11.80%)	(7.30%)
Manufacturing production deduction	(2.50%)	(2.40%)	(2.20%)
Officers’ compensation	0.20%	0.40%	1.10%
Adjustment to unrecognized tax benefits	0.30%	0.30%	(0.60%)
Foreign rate differential	(3.20%)	(3.10%)	(3.10%)
Research and experimentation tax credit	(1.30%)	(7.40%)	0.00%
Retiree medical expense	0.00%	0.00%	(2.00%)
Valuation allowance	(0.60%)	2.20%	4.00%
Other items	(0.60%)	4.80%	2.10%
Effective tax rate	23.00%	17.20%	26.70%