Summary of Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues
Lime and limestone operations	$ 33,564	$ 38,096	$ 32,376	$ 33,154	$ 30,797	$ 36,452	$ 31,779	$ 29,362	$ 137,190	$ 128,390	$ 144,567
Natural gas interests	602	554	504	432	497	577	671	702	2,092	2,447	5,274
Revenues	34,166	38,650	32,880	33,586	31,294	37,029	32,450	30,064	139,282	130,837	149,841
Gross profit (loss)
Gross profit (loss), Lime and limestone operations	7,355	10,503	7,245	7,929	5,575	10,320	6,809	5,697
Gross profit (loss), Natural gas interests	79	66	(4)	(81)	(105)	47	204	167
Gross profit (loss)	7,434	10,569	7,241	7,848	5,470	10,367	7,013	5,864	33,092	28,714	36,791
Net income	$ 3,920	$ 6,081	$ 3,687	$ 4,066	$ 2,286	$ 5,676	$ 2,559	$ 2,365	$ 17,754	$ 12,886	$ 19,367
Basic income per common share (in dollars per share)	$ 0.70	$ 1.09	$ 0.66	$ 0.73	$ 0.41	$ 1.01	$ 0.46	$ 0.42	$ 3.19	$ 2.30	$ 3.47
Diluted income per common share (in dollars per share)	$ 0.70	$ 1.09	$ 0.66	$ 0.73	$ 0.41	$ 1.01	$ 0.46	$ 0.42	$ 3.19	$ 2.30	$ 3.47