Derivatives (Fair Value Of Derivative Instruments And Locations In Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 721	$ 0
Non-current derivative assets	0	377
Total derivatives assets	721	377
Current derivative liabilities	7,763	21,564
Non-current derivative liabilities	0	415
Total derivative liabilities	7,763	21,979
Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Current derivative assets	721	0
Non-current derivative assets	0	377
Current derivative liabilities	7,763	21,564
Non-current derivative liabilities	$ 0	$ 415