Summary of Quarterly Financial Data (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues
Lime and limestone operations	$ 34,341	$ 37,855	$ 37,320	$ 35,051	$ 28,666	$ 35,498	$ 33,684	$ 30,155	$ 144,567	$ 128,003	$ 131,404
Natural gas interests	1,060	1,218	1,356	1,640	1,443	1,401	1,488	1,430	5,274	5,762	7,121
Revenues	35,401	39,073	38,676	36,691	30,109	36,899	35,172	31,585	149,841	133,765	138,525
Gross profit
Gross profit, Lime and limestone operations	7,321	9,271	9,704	7,662	5,474	8,409	8,363	5,667
Gross profit, Natural gas interests	572	612	719	930	961	701	601	624
Gross profit	7,893	9,883	10,423	8,592	6,435	9,110	8,964	6,291	36,791	30,800	33,438
Net income	$ 3,731	$ 5,426	$ 5,718	$ 4,492	$ 2,628	$ 4,789	$ 4,626	$ 2,757	$ 19,367	$ 14,800	$ 16,423
Basic income per common share (in dollars per share)	$ 0.67	$ 0.97	$ 1.03	$ 0.81	$ 0.47	$ 0.86	$ 0.83	$ 0.50	$ 3.47	$ 2.66	$ 2.88
Diluted income per common share (in dollars per share)	$ 0.67	$ 0.97	$ 1.03	$ 0.80	$ 0.47	$ 0.86	$ 0.83	$ 0.50	$ 3.47	$ 2.66	$ 2.87