Intangible Assets (Schedule of Components of Intangible Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 398,607	$ 396,823
Accumulated Amortization	219,852	214,417
Carrying Value	178,755	182,406
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	30,684	28,900
Accumulated Amortization	14,213	13,483
Carrying Value	16,471	15,417
Sodium Minerals & Sulfur Services
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	134,132	134,132
Accumulated Amortization	130,255	129,110
Carrying Value	3,877	5,022
Sodium Minerals & Sulfur Services \| Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	94,654	94,654
Accumulated Amortization	93,033	92,493
Carrying Value	1,621	2,161
Sodium Minerals & Sulfur Services \| Licensing agreements
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	38,678	38,678
Accumulated Amortization	37,066	36,528
Carrying Value	1,612	2,150
Sodium Minerals & Sulfur Services \| Non-compete agreement
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	800	800
Accumulated Amortization	156	89
Carrying Value	644	711
Onshore Facilities & Transportation
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	48,690	48,690
Accumulated Amortization	40,144	40,015
Carrying Value	8,546	8,675
Onshore Facilities & Transportation \| Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	35,430	35,430
Accumulated Amortization	35,093	35,082
Carrying Value	337	348
Onshore Facilities & Transportation \| Intangibles associated with lease
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	13,260	13,260
Accumulated Amortization	5,051	4,933
Carrying Value	8,209	8,327
Marine Transportation
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	27,000	27,000
Accumulated Amortization	13,050	11,700
Carrying Value	13,950	15,300
Offshore pipeline transportation
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	158,101	158,101
Accumulated Amortization	22,190	20,109
Carrying Value	$ 135,911	$ 137,992

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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