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