Unaudited Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenues	$ 61,380	$ 62,166	$ 184,601	$ 183,387
Cost and expenses
Cost of sales (exclusive of items shown separately below)	44,983	49,406	129,208	141,597
Asset retirement obligation accretion	128	124	383	370
Depreciation and amortization	5,353	3,348	14,291	8,741
Selling, general and administrative	4,464	3,484	13,127	10,608
Total cost and expenses	54,928	56,362	157,009	161,316
Operating income	6,452	5,804	27,592	22,071
Other income	573	1,036	1,063	2,038
Interest expense, net	(342)	(566)	(951)	(980)
Income before taxes	6,683	6,274	27,704	23,129
Income tax expense	1,133	63	4,658	1,448
Net income	$ 5,550	$ 6,211	$ 23,046	$ 21,681
Earnings Per Share
Basic earnings (in dollars per share)	$ 0.14	$ 0.15	$ 0.56	$ 0.54
Diluted earnings (in dollars per share)	$ 0.14	$ 0.15	$ 0.56	$ 0.54
Weighted average common shares outstanding
Basic weighted average shares outstanding (in shares)	40,936	40,082	40,804	40,024
Diluted weighted average shares outstanding (in shares)	40,936	40,329	40,804	40,271