Income Taxes (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Tax Contingency [Line Items]
Income from continuing operations before income tax provision:	$ 15,484,000	$ 13,675,000	$ 28,564,000	$ 25,255,000
Statutory taxes at 35%	5,419,000	4,786,000	9,997,000	8,839,000
Other	(727,000)	(344,000)	(729,000)	(323,000)
Tax Adjustments, Settlements, and Unusual Provisions	(727,000)	(344,000)	(729,000)	(323,000)
NACoal percentage depletion	(1,728,000)	(1,462,000)	(3,025,000)	(2,411,000)
Other	195,000	319,000	427,000	619,000
Effective Income Tax Rate Reconciliation Permanent Items	(1,533,000)	(1,143,000)	(2,598,000)	(1,792,000)
Income tax provision	3,159,000	3,299,000	6,670,000	6,724,000
Effective income tax rate	20.40%	24.10%	23.40%	26.60%
Statutory income tax rate, percent	35.00%	35.00%	35.00%	35.00%
Reed Minerals
Income Tax Contingency [Line Items]
Liability for uncertain tax positions	2,500,000		2,500,000
Long-term indemnification asset	$ 1,800,000		$ 1,800,000