Business Segments - Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Total revenue	$ 198,883	$ 240,033
Depreciation and Amortization	15,239	14,901
Operating Income (Loss) after Eliminations	15,600	9,606
Capital Expenditures and Plant Turnaround Costs	10,761	10,299
Terminalling and storage
Segment Reporting Information [Line Items]
Total revenue	49,408	54,171
Depreciation and Amortization	7,456	7,837
Operating Income (Loss) after Eliminations	758	4,815
Capital Expenditures and Plant Turnaround Costs	3,745	5,345
Transportation
Segment Reporting Information [Line Items]
Total revenue	38,941	37,795
Depreciation and Amortization	4,280	3,570
Operating Income (Loss) after Eliminations	(5,021)	(3,880)
Capital Expenditures and Plant Turnaround Costs	3,926	2,461
Sulfur services
Segment Reporting Information [Line Items]
Total revenue	28,323	31,593
Depreciation and Amortization	2,894	2,868
Operating Income (Loss) after Eliminations	13,858	6,380
Capital Expenditures and Plant Turnaround Costs	2,985	2,206
Natural gas liquids
Segment Reporting Information [Line Items]
Total revenue	82,211	116,474
Depreciation and Amortization	609	626
Operating Income (Loss) after Eliminations	10,377	6,858
Capital Expenditures and Plant Turnaround Costs	105	287
Operating Revenues
Segment Reporting Information [Line Items]
Total revenue	206,859	249,145
Operating Revenues | Terminalling and storage
Segment Reporting Information [Line Items]
Total revenue	51,134	55,892
Operating Revenues | Transportation
Segment Reporting Information [Line Items]
Total revenue	45,174	45,186
Operating Revenues | Sulfur services
Segment Reporting Information [Line Items]
Total revenue	28,336	31,593
Operating Revenues | Natural gas liquids
Segment Reporting Information [Line Items]
Total revenue	82,215	116,474
Intersegment Revenues Eliminations
Segment Reporting Information [Line Items]
Total revenue	(7,976)	(9,112)
Intersegment Revenues Eliminations | Terminalling and storage
Segment Reporting Information [Line Items]
Total revenue	(1,726)	(1,721)
Intersegment Revenues Eliminations | Transportation
Segment Reporting Information [Line Items]
Total revenue	(6,233)	(7,391)
Intersegment Revenues Eliminations | Sulfur services
Segment Reporting Information [Line Items]
Total revenue	(13)	0
Intersegment Revenues Eliminations | Natural gas liquids
Segment Reporting Information [Line Items]
Total revenue	(4)	0
Indirect selling, general and administrative
Segment Reporting Information [Line Items]
Depreciation and Amortization	0	0
Operating Income (Loss) after Eliminations	(4,372)	(4,567)
Capital Expenditures and Plant Turnaround Costs	$ 0	$ 0