Revenue from Contracts with Customers - Schedule of Changes in Deferred Revenue (Detail) $ in Thousands	6 Months Ended
Jun. 30, 2018 USD ($)
Deferred Revenue Arrangement [Line Items]
Opening balance	$ 168,757
Deferral of revenue	106,506
Recognition of unearned revenue	(92,470)
Other	(970)
Ending balance	$ 181,823

Amount of deferred revenue recognized for transactions arising during the current reporting period. Deferred revenue is a liability as of the balance sheet date related to a revenue producing activity for which revenue has not yet been recognized. Generally, an Entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

No definition available.

Name:	us-gaap_DeferredRevenueAdditions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration