Quarterly report pursuant to Section 13 or 15(d)

Derivative Financial Instruments (Schedule Of Contracts Designated As Hedged Instruments) (Details)

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Derivative Financial Instruments (Schedule Of Contracts Designated As Hedged Instruments) (Details)
€ in Thousands, £ in Thousands, NOK in Thousands, CAD in Thousands
9 Months Ended 12 Months Ended
Sep. 30, 2017
NOK
Dec. 31, 2016
GBP (£)
Sep. 30, 2017
GBP (£)
Sep. 30, 2017
EUR (€)
Sep. 30, 2017
CAD
Dec. 31, 2016
EUR (€)
Dec. 31, 2016
CAD
Norwegian Kroner [Member]              
Foreign Exchange Contracts [Line Items]              
Foreign exchange contracts, Notional Amount | NOK NOK 7,449            
Norwegian Kroner [Member] | Designated as Hedging Instrument [Member]              
Foreign Exchange Contracts [Line Items]              
Derivative, Maturity Date Feb. 01, 2018            
Canadian Dollars [Member]              
Foreign Exchange Contracts [Line Items]              
Foreign exchange contracts, Notional Amount | CAD         CAD 13,345   CAD 11,001
Canadian Dollars [Member] | Designated as Hedging Instrument [Member]              
Foreign Exchange Contracts [Line Items]              
Derivative, Maturity Date Feb. 01, 2019 Feb. 01, 2018          
British Pounds [Member]              
Foreign Exchange Contracts [Line Items]              
Foreign exchange contracts, Notional Amount | £   £ 1,842 £ 2,343        
British Pounds [Member] | Designated as Hedging Instrument [Member]              
Foreign Exchange Contracts [Line Items]              
Derivative, Maturity Date Feb. 01, 2019 Feb. 01, 2018          
Euro [Member]              
Foreign Exchange Contracts [Line Items]              
Foreign exchange contracts, Notional Amount | €       € 22,200   € 14,366  
Euro [Member] | Designated as Hedging Instrument [Member]              
Foreign Exchange Contracts [Line Items]              
Derivative, Maturity Date Feb. 01, 2019 Feb. 01, 2018