Derivatives (Derivatives Gains and Losses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Not designated as hedging | Cost of sales
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Losses) on commodity derivatives included in cost of sales and merchandising revenues	$ 4,236	$ 5,417	$ (15,012)
Not designated as hedging | Interest rate contract | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Losses) on commodity derivatives included in cost of sales and merchandising revenues	1,115	1,286
Not designated as hedging | Foreign Exchange Contract | Other Income
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Losses) on commodity derivatives included in cost of sales and merchandising revenues	(1,548)	539
Designated as Hedging Instrument | Interest rate contract
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate derivative gains (losses) included in OCI	(168)	0
Designated as Hedging Instrument | Interest rate contract | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate derivative gains (losses) included in Interest income (expense)	$ 158	$ 0