Receivables (Schedule of Trade Accounts Receivables Net) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts Receivable, Net, Current [Abstract]
Accounts receivable - trade	$ 503,917	$ 231,187
Allowance for doubtful accounts	(8,468)	(6,505)	$ (1,446)	$ (2,973)
Accounts receivable - trade, net	$ 495,449	$ 224,682