Derivative Instruments (Fair Values of Derivative Instruments in Consolidated Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Accrued Liabilities
Derivatives, Fair Value [Line Items]
Total derivative liabilities	$ 7,244	$ 13,694
Accounts Receivable
Derivatives, Fair Value [Line Items]
Total derivative assets	9,050	14,427
Forward Contracts [Member] | Accrued Liabilities
Derivatives, Fair Value [Line Items]
Designated as hedging instruments, Derivative Liabilities	0	399
Not designated as hedging instruments, Derivative Liabilities	7,244	13,295
Forward Contracts [Member] | Accounts Receivable
Derivatives, Fair Value [Line Items]
Designated as hedging instruments, Derivative Assets	6,720	13,032
Not designated as hedging instruments, Derivative Assets	$ 2,330	$ 1,395