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Derivative Financial Instruments (Schedule Of Contracts Not Designated As Hedged Instruments) (Details)
€ in Thousands, £ in Thousands, kr in Thousands, $ in Thousands
 6 Months Ended
Jun. 30, 2018
GBP (£)
Jun. 30, 2018
EUR (€)
Jun. 30, 2018
CAD ($)
Dec. 31, 2017
NOK (kr)
Dec. 31, 2017
GBP (£)
Dec. 31, 2017
EUR (€)
Dec. 31, 2017
CAD ($)
Norwegian Kroner [Member]              
Foreign Exchange Contracts [Line Items]              
Foreign exchange contracts, Notional Amount | kr       kr 2,629      
Canadian Dollars [Member]              
Foreign Exchange Contracts [Line Items]              
Foreign exchange contracts, Notional Amount | $     $ 10,535       $ 9,538
British Pounds [Member]              
Foreign Exchange Contracts [Line Items]              
Foreign exchange contracts, Notional Amount £ 266       £ 1,737    
British Pounds [Member] | Not Designated as Hedging Instrument [Member]              
Foreign Exchange Contracts [Line Items]              
Foreign exchange contracts, Notional Amount £ 465            
Derivative, Maturity Date Feb. 01, 2019            
Euro [Member]              
Foreign Exchange Contracts [Line Items]              
Foreign exchange contracts, Notional Amount | €   € 11,693       € 15,928