Summary of Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Lime and limestone operations	$ 34,702	$ 36,428	$ 35,965	$ 35,517	$ 33,564	$ 38,096	$ 32,376	$ 33,154	$ 142,612	$ 137,190	$ 128,390
Natural gas interests	537	506	553	636	602	554	504	432	2,232	2,092	2,447
Revenues	35,239	36,934	36,518	36,153	34,166	38,650	32,880	33,586	144,844	139,282	130,837
Gross profit (loss)
Gross profit (loss), Lime and limestone operations	7,434	9,476	8,722	8,020	7,355	10,503	7,245	7,929
Gross profit (loss), Natural gas interests	318	76	116	218	79	66	(4)	(81)
Gross profit (loss)	7,752	9,552	8,838	8,238	7,434	10,569	7,241	7,848	34,380	33,092	28,714
Net income	$ 11,583	$ 5,667	$ 5,278	$ 4,620	$ 3,920	$ 6,081	$ 3,687	$ 4,066	$ 27,148	$ 17,754	$ 12,886
Basic income per common share (in dollars per share)	$ 2.08	$ 1.02	$ 0.95	$ 0.83	$ 0.70	$ 1.09	$ 0.66	$ 0.73	$ 4.87	$ 3.19	$ 2.30
Diluted income per common share (in dollars per share)	$ 2.07	$ 1.01	$ 0.94	$ 0.83	$ 0.70	$ 1.09	$ 0.66	$ 0.73	$ 4.86	$ 3.19	$ 2.30