Business Segments - Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information
Revenues	$ 797,963	$ 1,018,878	$ 882,431
Depreciation and Amortization	49,895	56,280	56,751
Operating Income (Loss) after Eliminations	66,724	51,263	57,280
Operating Segments
Segment Reporting Information
Revenues	824,243	1,051,687	911,958
Depreciation and Amortization	49,895	56,280	56,751
Operating Income (Loss) after Eliminations	66,724	51,263	57,280
Capital Expenditures and Plant Turnaround Costs	40,136	31,133	22,929
Intersegment Eliminations
Segment Reporting Information
Revenues	(26,280)	(32,809)	(29,527)
Indirect selling, general, and administrative
Segment Reporting Information
Operating Income (Loss) after Eliminations	(16,030)	(16,914)	(16,129)
Terminalling and storage
Segment Reporting Information
Revenues	86,514	80,193	75,223
Terminalling and storage | Operating Segments
Segment Reporting Information
Revenues	95,459	92,612	87,816
Depreciation and Amortization	21,030	26,094	25,441
Operating Income (Loss) after Eliminations	5,676	(11,102)	(9,161)
Capital Expenditures and Plant Turnaround Costs	13,168	15,308	8,354
Terminalling and storage | Intersegment Eliminations
Segment Reporting Information
Revenues	(8,945)	(12,419)	(12,593)
Specialty products
Segment Reporting Information
Revenues	346,777	540,513	517,852
Specialty products | Operating Segments
Segment Reporting Information
Revenues	346,863	540,636	517,920
Depreciation and Amortization	3,296	4,520	5,159
Operating Income (Loss) after Eliminations	30,335	24,142	58,044
Capital Expenditures and Plant Turnaround Costs	2,519	1,349	1,765
Specialty products | Intersegment Eliminations
Segment Reporting Information
Revenues	(86)	(123)	(68)
Sulfur services
Segment Reporting Information
Revenues	140,995	179,164	145,042
Sulfur services | Operating Segments
Segment Reporting Information
Revenues	140,995	179,164	145,042
Depreciation and Amortization	10,690	11,099	10,432
Operating Income (Loss) after Eliminations	30,436	34,146	32,972
Capital Expenditures and Plant Turnaround Costs	16,851	6,857	7,813
Sulfur services | Intersegment Eliminations
Segment Reporting Information
Revenues	0	0	0
Transportation
Segment Reporting Information
Revenues	223,677	219,008	144,314
Transportation | Operating Segments
Segment Reporting Information
Revenues	240,926	239,275	161,180
Depreciation and Amortization	14,879	14,567	15,719
Operating Income (Loss) after Eliminations	16,307	20,991	(8,446)
Capital Expenditures and Plant Turnaround Costs	7,598	7,619	4,997
Transportation | Intersegment Eliminations
Segment Reporting Information
Revenues	$ (17,249)	$ (20,267)	$ (16,866)