Financial Instruments and Risk Management (Gross Notional Amount of Outstanding Derivatives) (Details) - Foreign Exchange Forward [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Currency forward contracts	$ 448,448	$ 206,000
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Currency forward contracts	$ 231,161	$ 184,940

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant