Commitments and Contingencies (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Letter of credit [Member]
Letters of credit outstanding	$ 64,225	$ 59,350

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