Derivative Financial Instruments (Schedule Of Contracts Designated As Hedged Instruments) (Details) € in Thousands, £ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 GBP (£)	Dec. 31, 2016 GBP (£)	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 CAD ($)	Dec. 31, 2016 EUR (€)	Dec. 31, 2016 CAD ($)
Norwegian Kroner [Member]
Foreign Exchange Contracts [Line Items]
Foreign exchange contracts, Notional Amount				$ 2,629
Derivative, Maturity Date	Feb. 01, 2018
Canadian Dollars [Member]
Foreign Exchange Contracts [Line Items]
Foreign exchange contracts, Notional Amount				$ 9,538		$ 11,001
Derivative, Maturity Date	Feb. 01, 2019	Feb. 01, 2018
British Pounds [Member]
Foreign Exchange Contracts [Line Items]
Foreign exchange contracts, Notional Amount \| £	£ 1,737	£ 1,842
Derivative, Maturity Date	Feb. 01, 2019	Feb. 01, 2018
Euro [Member]
Foreign Exchange Contracts [Line Items]
Foreign exchange contracts, Notional Amount \| €			€ 15,928		€ 14,366
Derivative, Maturity Date	Feb. 01, 2019	Feb. 01, 2018