Derivatives (Schedule of Effect on Operating Results) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Commodity derivatives - futures and call options | Cost of Goods and Services Sold
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	$ (7,434)	$ (1,698)
Preferred Distribution Rate Reset Election | Other expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	(2,976)	(1,906)
Contracts designated as hedges under accounting guidance | Commodity derivatives - futures and call options | Cost of Goods and Services Sold | Onshore facilities and transportation product costs
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	(742)	(1,366)
Contracts not considered hedges under accounting guidance | Commodity derivatives - futures and call options | Cost of Goods and Services Sold | Onshore facilities and transportation product costs, sodium minerals and sulfur services operating costs
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	(6,692)	(332)
Contracts not considered hedges under accounting guidance | Natural Gas Swap Liability | Cost of Goods and Services Sold | Sodium minerals and sulfur services operating costs
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Income	$ 1,519	$ (275)