Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenue	$ 36,374	$ 65,761	$ 78,310	$ 123,221
Cost and expenses
Cost of sales (exclusive of items shown separately below)	30,134	43,219	61,069	84,225
Asset retirement obligation accretion	159	128	300	256
Depreciation and amortization	5,341	4,822	10,343	8,938
Selling, general and administrative	5,039	4,703	9,756	8,664
Total cost and expenses	40,673	52,872	81,468	102,083
Operating income (loss)	(4,299)	12,889	(3,158)	21,138
Other income	8,504	194	9,714	492
Interest expense, net	(293)	(302)	(572)	(609)
Income before tax	3,912	12,781	5,984	21,021
Income tax expense	1,260	2,168	1,370	3,525
Net income	$ 2,652	$ 10,613	$ 4,614	$ 17,496
Earnings per common share
Basic earnings (in dollars per share)	$ 0.06	$ 0.26	$ 0.11	$ 0.43
Diluted earnings (in dollars per share)	$ 0.06	$ 0.26	$ 0.11	$ 0.43
Weighted average common shares outstanding
Basic weighted average shares outstanding (in shares)	42,704	40,869	42,232	40,737
Diluted weighted average shares outstanding (in shares)	42,704	40,965	42,232	40,810