Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Derivative Financial Instruments (Schedule Of Contracts Designated As Hedged Instruments) (Details) - Designated as Hedging Instrument [Member]
€ in Thousands, £ in Thousands, kr in Thousands, $ in Thousands
9 Months Ended 12 Months Ended
Sep. 30, 2018
EUR (€)
Dec. 31, 2017
NOK (kr)
Sep. 30, 2018
CAD ($)
Dec. 31, 2017
GBP (£)
Dec. 31, 2017
EUR (€)
Dec. 31, 2017
CAD ($)
Norwegian Kroner [Member]            
Foreign Exchange Contracts [Line Items]            
Foreign exchange contracts, Notional Amount | kr   kr 2,629        
Derivative, Maturity Date   Feb. 01, 2018        
Canadian Dollars [Member]            
Foreign Exchange Contracts [Line Items]            
Foreign exchange contracts, Notional Amount | $     $ 9,129     $ 9,538
Derivative, Maturity Date Aug. 01, 2019 Feb. 01, 2019        
British Pounds [Member]            
Foreign Exchange Contracts [Line Items]            
Foreign exchange contracts, Notional Amount | £       £ 1,737    
Derivative, Maturity Date   Feb. 01, 2019        
Euro [Member]            
Foreign Exchange Contracts [Line Items]            
Foreign exchange contracts, Notional Amount | € € 10,244       € 15,928  
Derivative, Maturity Date Aug. 01, 2019 Feb. 01, 2019