Business Segments - Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information
Total revenue	$ 152,533	$ 177,900	$ 492,054	$ 605,256
Depreciation and Amortization	15,276	15,009	45,858	44,997
Operating Income (Loss) after Eliminations	11,013	25,461	34,573	40,077
Capital Expenditures and Plant Turnaround Costs	5,214	7,867	21,983	26,793
Terminalling and storage
Segment Reporting Information
Total revenue	46,365	53,746	141,207	160,665
Depreciation and Amortization	7,294	7,690	22,022	23,353
Operating Income (Loss) after Eliminations	6,426	5,393	10,153	14,462
Capital Expenditures and Plant Turnaround Costs	1,863	1,616	8,885	9,465
Transportation
Segment Reporting Information
Total revenue	31,938	40,211	102,364	119,327
Depreciation and Amortization	4,412	3,877	13,020	11,225
Operating Income (Loss) after Eliminations	(2,673)	0	(9,772)	(6,509)
Capital Expenditures and Plant Turnaround Costs	1,785	2,449	6,483	5,656
Sulfur services
Segment Reporting Information
Total revenue	21,880	23,072	83,623	90,521
Depreciation and Amortization	2,953	2,831	8,978	8,553
Operating Income (Loss) after Eliminations	7,115	2,384	29,787	16,292
Capital Expenditures and Plant Turnaround Costs	1,393	3,138	6,267	9,781
Natural gas liquids
Segment Reporting Information
Total revenue	52,350	60,871	164,860	234,743
Depreciation and Amortization	617	611	1,838	1,866
Operating Income (Loss) after Eliminations	4,668	22,199	17,661	29,513
Capital Expenditures and Plant Turnaround Costs	173	664	348	1,891
Operating Revenues
Segment Reporting Information
Total revenue	158,130	183,950	510,944	627,933
Operating Revenues | Terminalling and storage
Segment Reporting Information
Total revenue	48,188	55,376	146,298	165,619
Operating Revenues | Transportation
Segment Reporting Information
Total revenue	35,712	44,631	116,145	137,050
Operating Revenues | Sulfur services
Segment Reporting Information
Total revenue	21,880	23,072	83,636	90,521
Operating Revenues | Natural gas liquids
Segment Reporting Information
Total revenue	52,350	60,871	164,865	234,743
Intersegment Revenues Eliminations
Segment Reporting Information
Total revenue	(5,597)	(6,050)	(18,890)	(22,677)
Intersegment Revenues Eliminations | Terminalling and storage
Segment Reporting Information
Total revenue	(1,823)	(1,630)	(5,091)	(4,954)
Intersegment Revenues Eliminations | Transportation
Segment Reporting Information
Total revenue	(3,774)	(4,420)	(13,781)	(17,723)
Intersegment Revenues Eliminations | Sulfur services
Segment Reporting Information
Total revenue	0	0	(13)	0
Intersegment Revenues Eliminations | Natural gas liquids
Segment Reporting Information
Total revenue	0	0	(5)	0
Indirect selling, general and administrative
Segment Reporting Information
Depreciation and Amortization	0	0	0	0
Operating Income (Loss) after Eliminations	(4,523)	(4,515)	(13,256)	(13,681)
Capital Expenditures and Plant Turnaround Costs	$ 0	$ 0	$ 0	$ 0