Intangible Assets, Goodwill and Other Assets (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Intangible Assets, Goodwill And Other Assets [Line Items]
Amortization of expense of intangible assets	$ 23,600,000	$ 24,300,000	$ 20,000,000
Goodwill	325,046,000	325,046,000
Impairment of goodwill	0	0	0
Amortization of CO2 assets	1,300,000	3,900,000	5,900,000
Sodium Minerals and Sulfur Services
Intangible Assets, Goodwill And Other Assets [Line Items]
Goodwill	301,900,000	301,900,000
Impairment of goodwill	0	0	0
Onshore Facilities and Transportation
Intangible Assets, Goodwill And Other Assets [Line Items]
Goodwill	23,100,000	23,100,000
Impairment of goodwill	$ 0	$ 0	$ 0