Derivative Instruments (Fair Values of Derivative Instruments in Consolidated Balance Sheets) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accrued liabilities
Derivatives, Fair Value [Line Items]
Total derivative liabilities	$ 6,493	$ 10,108
Accounts receivable, net
Derivatives, Fair Value [Line Items]
Total derivative assets	4,872	3,145
Forward Contracts [Member] | Accrued liabilities
Derivatives, Fair Value [Line Items]
Not designated as hedging instruments, Derivative Liabilities	3,446	6,549
Forward Contracts [Member] | Accounts receivable, net
Derivatives, Fair Value [Line Items]
Not designated as hedging instruments, Derivative Assets	2,439	3,145
Forward Contracts [Member] | Deferred charges and other assets, net
Derivatives, Fair Value [Line Items]
Not designated as hedging instruments, Derivative Assets	2,433	0
Commodity Forward Contracts [Member] | Other liabilities
Derivatives, Fair Value [Line Items]
Not designated as hedging instruments, Derivative Liabilities	$ 3,047	$ 3,559