Income Taxes (Reconciliation of the Federal Statutory and Effective Income Tax Rate) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Income from continuing operations before income tax provision	$ 55,720,000	$ 58,028,000	$ 112,221,000
Statutory taxes at 35.0%	19,502,000	20,310,000	39,277,000
State and local income taxes	136,000	1,568,000	1,925,000
Non-deductible expenses	1,081,000	1,112,000	1,336,000
Percentage depletion	(8,057,000)	(4,963,000)	(6,895,000)
R&D and other federal credits	(1,173,000)	(132,000)	(206,000)
Other, net	(219,000)	(2,030,000)	(2,686,000)
Income tax provision	11,270,000	15,865,000	32,751,000
Effective income tax rate	20.20%	27.30%	29.20%
Statutory tax rate	35.00%	35.00%	35.00%
Cumulative unremitted earnings of foreign subsidiaries	8,800,000
Cumulative deferred tax liabilities of unremitted foreign earnings	$ 168,000	$ 101,000