Intangible Assets (Schedule of Components of Intangible Assets) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 398,997	$ 396,823
Accumulated Amortization	225,312	214,417
Carrying Value	173,685	182,406
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	31,074	28,900
Accumulated Amortization	14,970	13,483
Carrying Value	16,104	15,417
Sodium Minerals & Sulfur Services
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	134,132	134,132
Accumulated Amortization	131,399	129,110
Carrying Value	2,733	5,022
Sodium Minerals & Sulfur Services \| Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	94,654	94,654
Accumulated Amortization	93,574	92,493
Carrying Value	1,080	2,161
Sodium Minerals & Sulfur Services \| Licensing agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	38,678	38,678
Accumulated Amortization	37,603	36,528
Carrying Value	1,075	2,150
Sodium Minerals & Sulfur Services \| Non-compete agreement
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	800	800
Accumulated Amortization	222	89
Carrying Value	578	711
Onshore Facilities & Transportation
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	48,690	48,690
Accumulated Amortization	40,273	40,015
Carrying Value	8,417	8,675
Onshore Facilities & Transportation \| Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	35,430	35,430
Accumulated Amortization	35,103	35,082
Carrying Value	327	348
Onshore Facilities & Transportation \| Intangibles associated with lease
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	13,260	13,260
Accumulated Amortization	5,170	4,933
Carrying Value	8,090	8,327
Marine Transportation
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	27,000	27,000
Accumulated Amortization	14,400	11,700
Carrying Value	12,600	15,300
Offshore pipeline transportation
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	158,101	158,101
Accumulated Amortization	24,270	20,109
Carrying Value	$ 133,831	$ 137,992

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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-Publisher FASB
-Name Accounting Standards Codification
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