Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Revenue	$ 41,935	$ 57,460
Cost and expenses
Cost of sales (exclusive of items shown separately below)	30,934	41,006
Asset retirement obligation accretion	141	128
Depreciation and amortization	5,002	4,116
Selling, general and administrative	4,717	3,960
Total cost and expenses	40,794	49,210
Operating income	1,141	8,250
Other income	1,210	298
Interest expense, net	(279)	(307)
Income before tax	2,072	8,241
Income tax expense	110	1,358
Net income	$ 1,962	$ 6,883
Earnings (loss) per common share
Basic earnings (in dollars per share)	$ 0.05	$ 0.17
Diluted earnings (in dollars per share)	$ 0.05	$ 0.17
Weighted average common shares outstanding
Basic weighted average shares outstanding (in shares)	41,760	40,604
Diluted weighted average shares outstanding (in shares)	41,760	40,652