Summary of Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue Recognition
Revenues	$ 34,634	$ 35,272	$ 39,242	$ 35,287	$ 35,239	$ 36,934	$ 36,518	$ 36,153	$ 144,435	$ 144,844	$ 139,282
Gross profit (loss)
Gross profit (loss), Lime and limestone operations	6,370	6,992	9,327	6,793	7,434	9,476	8,722	8,020
Gross profit (loss), Natural gas interests	246	204	310	244	318	76	116	218
Gross profit	6,616	7,196	9,637	7,037	7,752	9,552	8,838	8,238	30,486	34,380	33,092
Net income	$ 4,231	$ 4,554	$ 6,638	$ 4,262	$ 11,583	$ 5,667	$ 5,278	$ 4,620	$ 19,685	$ 27,148	$ 17,754
Basic income per common share (in dollars per share)	$ 0.76	$ 0.81	$ 1.19	$ 0.76	$ 2.08	$ 1.02	$ 0.95	$ 0.83	$ 3.52	$ 4.87	$ 3.19
Diluted income per common share (in dollars per share)	$ 0.75	$ 0.81	$ 1.18	$ 0.76	$ 2.07	$ 1.01	$ 0.94	$ 0.83	$ 3.51	$ 4.86	$ 3.19
Lime and limestone operations
Revenue Recognition
Revenues	$ 33,938	$ 34,713	$ 38,557	$ 34,714	$ 34,702	$ 36,428	$ 35,965	$ 35,517	$ 141,922	$ 142,612	$ 137,190
Natural gas interests
Revenue Recognition
Revenues	$ 696	$ 559	$ 685	$ 573	$ 537	$ 506	$ 553	$ 636	$ 2,513	$ 2,232	$ 2,092