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, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues
Lime and limestone operations	$ 30,212	$ 32,558	$ 34,729	$ 33,905	$ 30,462	$ 35,658	$ 33,382	$ 30,202	$ 131,404	$ 129,704	$ 125,169
Natural gas interests	1,671	1,558	1,769	2,123	3,032	3,524	3,458	2,864	7,121	12,878	7,425
Revenues	31,883	34,116	36,498	36,028	33,494	39,182	36,840	33,066	138,525	142,582	132,594
Gross profit
Gross profit, Lime and limestone operations	7,252	6,972	7,324	7,951	6,696	10,092	7,814	7,539
Gross profit, Natural gas interests	871	787	1,029	1,252	2,302	2,447	2,585	1,873
Gross profit	8,123	7,759	8,353	9,203	8,998	12,539	10,399	9,412	33,438	41,349	36,041
Net income	$ 3,792	$ 3,947	$ 4,060	$ 4,624	$ 4,515	$ 7,062	$ 5,795	$ 4,813	$ 16,423	$ 22,186	$ 18,040
Basic income per common share (in dollars per share)	$ 0.68	$ 0.71	$ 0.73	$ 0.75	$ 0.73	$ 1.12	$ 0.90	$ 0.75	$ 2.88	$ 3.50	$ 2.82
Diluted income per common share (in dollars per share)	$ 0.68	$ 0.71	$ 0.73	$ 0.75	$ 0.72	$ 1.11	$ 0.90	$ 0.75	$ 2.87	$ 3.49	$ 2.81