Intangible Assets, Goodwill and Other Assets (Schedule of Intangible Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 396,823	$ 395,692
Accumulated Amortization	214,417	190,805
Carrying Value	$ 182,406	204,887
Other
Finite-Lived Intangible Assets [Line Items]
Weighted Amortization Period in Years	5 years
Gross Carrying Amount	$ 28,900	28,569
Accumulated Amortization	13,483	10,622
Carrying Value	15,417	17,947
Sodium Minerals and Sulfur Services
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	134,132	133,332
Accumulated Amortization	129,110	123,960
Carrying Value	$ 5,022	9,372
Sodium Minerals and Sulfur Services | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Amortization Period in Years	5 years
Gross Carrying Amount	$ 94,654	94,654
Accumulated Amortization	92,493	89,756
Carrying Value	$ 2,161	4,898
Sodium Minerals and Sulfur Services | Licensing agreements
Finite-Lived Intangible Assets [Line Items]
Weighted Amortization Period in Years	6 years
Gross Carrying Amount	$ 38,678	38,678
Accumulated Amortization	36,528	34,204
Carrying Value	$ 2,150	4,474
Sodium Minerals and Sulfur Services | Non-compete agreement
Finite-Lived Intangible Assets [Line Items]
Weighted Amortization Period in Years	3 years
Gross Carrying Amount	$ 800	0
Accumulated Amortization	89	0
Carrying Value	711	0
Onshore Facilities and Transportation
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	48,690	48,690
Accumulated Amortization	40,015	38,135
Carrying Value	$ 8,675	10,555
Onshore Facilities and Transportation | Customer relationships
Finite-Lived Intangible Assets [Line Items]
Weighted Amortization Period in Years	5 years
Gross Carrying Amount	$ 35,430	35,430
Accumulated Amortization	35,082	33,676
Carrying Value	$ 348	1,754
Onshore Facilities and Transportation | Intangibles associated with lease
Finite-Lived Intangible Assets [Line Items]
Weighted Amortization Period in Years	15 years
Gross Carrying Amount	$ 13,260	13,260
Accumulated Amortization	4,933	4,459
Carrying Value	$ 8,327	8,801
Marine Transportation
Finite-Lived Intangible Assets [Line Items]
Weighted Amortization Period in Years	5 years
Gross Carrying Amount	$ 27,000	27,000
Accumulated Amortization	11,700	6,300
Carrying Value	$ 15,300	20,700
Offshore Pipeline Transportation
Finite-Lived Intangible Assets [Line Items]
Weighted Amortization Period in Years	19 years
Gross Carrying Amount	$ 158,101	158,101
Accumulated Amortization	20,109	11,788
Carrying Value	$ 137,992	$ 146,313