Guarantees (Details 1) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Guarantees [Abstract]
Letters of credit	$ 238,610	$ 240,420
Surety bonds	$ 111,007	$ 113,696

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

No definition available.

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant