Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue	$ 39,459	$ 61,380	$ 117,769	$ 184,601
Cost and expenses
Cost of sales (exclusive of items shown separately below)	35,689	44,983	96,758	129,208
Asset retirement obligation accretion	128	128	428	383
Depreciation and amortization	5,258	5,353	15,601	14,291
Selling, general and administrative	5,966	4,464	15,723	13,127
Total cost and expenses	47,041	54,928	128,510	157,009
Operating income (loss)	(7,582)	6,452	(10,741)	27,592
Other income	1,743	573	11,456	1,063
Interest expense, net	(344)	(342)	(915)	(951)
Income before tax	(6,183)	6,683	(200)	27,704
Income tax expense	(1,407)	1,133	(38)	4,658
Net income	$ (4,776)	$ 5,550	$ (162)	$ 23,046
Earnings per common share
Basic earnings (in dollars per share)	$ (0.11)	$ 0.14	$ 0.00	$ 0.56
Diluted earnings (in dollars per share)	$ (0.11)	$ 0.14	$ 0.00	$ 0.56
Weighted average common shares outstanding
Basic weighted average shares outstanding (in shares)	42,647	40,936	42,373	40,804
Diluted weighted average shares outstanding (in shares)	42,647	40,936	42,373	40,804