Accounts Receivable Factoring (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Transfers and Servicing [Abstract]
Continuing Involvement with Derecognized Transferred Financial Assets, Amount Outstanding	$ 96,588	$ 56,936
Continuing Involvement with Continued to be Recognized Transferred Financial Assets, Amount Outstanding	0	5,258
Amount Of Account Receivable Factoring Without Recourse	544,060	507,321
Amount Of Account Receivable Factoring With Recourse	23,794	24,053
Loss On Sale Of Accounts Receivable Without Recourse	1,904	1,575	$ 2,144
Loss On Sale Of Accounts Receivable With Recourse	$ 99	$ 257	$ 179