Business Segments - Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information
Total revenue	$ 211,258	$ 152,533	$ 596,525	$ 492,054
Depreciation and Amortization	13,945	15,276	42,862	45,858
Operating Income (Loss) after Eliminations	8,153	11,013	31,472	34,573
Capital Expenditures and Plant Turnaround Costs	4,297	5,214	14,409	21,983
Terminalling and storage
Segment Reporting Information
Total revenue	49,578	46,365	131,666	141,207
Depreciation and Amortization	7,049	7,294	21,150	22,022
Operating Income (Loss) after Eliminations	3,269	6,426	8,153	10,153
Capital Expenditures and Plant Turnaround Costs	2,087	1,863	6,258	8,885
Transportation
Segment Reporting Information
Total revenue	39,079	31,938	103,820	102,364
Depreciation and Amortization	3,710	4,412	12,039	13,020
Operating Income (Loss) after Eliminations	430	(2,673)	(7,782)	(9,772)
Capital Expenditures and Plant Turnaround Costs	1,086	1,785	2,702	6,483
Sulfur services
Segment Reporting Information
Total revenue	30,837	21,880	103,958	83,623
Depreciation and Amortization	2,594	2,953	7,882	8,978
Operating Income (Loss) after Eliminations	4,534	7,115	21,136	29,787
Capital Expenditures and Plant Turnaround Costs	1,104	1,393	4,968	6,267
Natural gas liquids
Segment Reporting Information
Total revenue	91,764	52,350	257,081	164,860
Depreciation and Amortization	592	617	1,791	1,838
Operating Income (Loss) after Eliminations	3,994	4,668	21,738	17,661
Capital Expenditures and Plant Turnaround Costs	20	173	481	348
Operating Revenues
Segment Reporting Information
Total revenue	216,395	158,130	612,509	510,944
Operating Revenues | Terminalling and storage
Segment Reporting Information
Total revenue	51,226	48,188	136,584	146,298
Operating Revenues | Transportation
Segment Reporting Information
Total revenue	42,568	35,712	114,886	116,145
Operating Revenues | Sulfur services
Segment Reporting Information
Total revenue	30,837	21,880	103,958	83,636
Operating Revenues | Natural gas liquids
Segment Reporting Information
Total revenue	91,764	52,350	257,081	164,865
Intersegment Revenues Eliminations
Segment Reporting Information
Total revenue	(5,137)	(5,597)	(15,984)	(18,890)
Intersegment Revenues Eliminations | Terminalling and storage
Segment Reporting Information
Total revenue	(1,648)	(1,823)	(4,918)	(5,091)
Intersegment Revenues Eliminations | Transportation
Segment Reporting Information
Total revenue	(3,489)	(3,774)	(11,066)	(13,781)
Intersegment Revenues Eliminations | Sulfur services
Segment Reporting Information
Total revenue	0	0	0	(13)
Intersegment Revenues Eliminations | Natural gas liquids
Segment Reporting Information
Total revenue	0	0	0	(5)
Indirect selling, general and administrative
Segment Reporting Information
Depreciation and Amortization	0	0	0	0
Operating Income (Loss) after Eliminations	(4,074)	(4,523)	(11,773)	(13,256)
Capital Expenditures and Plant Turnaround Costs	$ 0	$ 0	$ 0	$ 0