Guarantees (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Guarantees [Abstract]
Letters of credit	$ 253,259	$ 238,610
Surety bonds	$ 121,757	$ 111,007

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