Note Supplemental disclosure on the consolidated statments of cash flows (Additional Information) (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure - Additional Disclosures on Cash Flow Information and Non-Cash Activities [Abstract]
Cash Acquired From Acquisition	$ 0	$ 0	$ 731,279

The cash inflow associated with the acquisition of business during the period (for example, cash that was held by the acquired business).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

Name:	us-gaap_CashAcquiredFromAcquisition
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration