Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenue	$ 230,213	$ 227,574	$ 61,036
Cost and expenses
Cost of sales (exclusive of items shown separately below)	162,470	176,555	60,521
Other operating costs and expenses			258
Asset retirement obligation accretion	511	494	405
Depreciation and amortization	19,521	12,423	3,154
Selling, general and administrative	18,179	14,006	12,591
Total cost and expenses	200,681	203,478	76,929
Operating income (loss)	29,532	24,096	(15,893)
Other income	1,758	2,518	204
Interest expense, net	(1,193)	(1,427)
Interest income			272
Income (loss) before tax	30,097	25,187	(15,417)
Income tax expense	5,163	113
Net income (loss)	$ 24,934	$ 25,074	$ (15,417)
Earnings (loss) per common share
Basic earnings (in dollars per share)	$ 0.61	$ 0.63	$ (0.41)
Diluted earnings (in dollars per share)	$ 0.61	$ 0.62	$ (0.41)
Weighted average common shares outstanding
Basic weighted average shares outstanding (in shares)	40,838	40,039	37,578
Diluted weighted average shares outstanding (in shares)	40,838	40,263	37,578