Commitments and Contingencies (Letters of Credit and Guarantees) - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Letters of credit outstanding	$ 0.9	$ 2.3
License bonds outstanding amount	$ 2.9	$ 2.5

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