Credit Arrangements - Additional Information (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Line of Credit Facility [Abstract]
Standby letters of credit	$ 75,311

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