Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Goodwill (Schedule of Changes in the Carrying Amount of Goodwill) (Details)

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Goodwill (Schedule of Changes in the Carrying Amount of Goodwill) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Goodwill [Abstract].    
Goodwill as of January 1 $ 385,629 $ 383,853
Translation differences 1,500 1,700
Goodwill as of December 31 $ 387,108 $ 385,629