Annual report pursuant to Section 13 and 15(d)

Financial Instruments and Risk Management (Gross Notional Amount of Outstanding Derivatives) (Details)

v3.10.0.1
Financial Instruments and Risk Management (Gross Notional Amount of Outstanding Derivatives) (Details) - Foreign Exchange Forward [Member] - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Designated as Hedging Instrument [Member]    
Derivatives, Fair Value [Line Items]    
Currency forward contracts $ 399,348 $ 448,448
Not Designated as Hedging Instrument [Member]    
Derivatives, Fair Value [Line Items]    
Currency forward contracts $ 379,701 $ 231,161