Capital Stock - Additional Information (Detail)		12 Months Ended
Nov. 13, 2017 shares	Dec. 31, 2017 Vote shares
Equity [Abstract]
Preference shares included in authorized capital stock		99,760,000
Shares issued or outstanding		0
Number of votes per share \| Vote		1
Number of common stock shares to be purchased under the Bid	35,800,000
Percentage of issued and outstanding common shares	10.00%
Commencement date of Bid		Nov. 15, 2017
Termination date of Bid		Nov. 14, 2018

Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_PreferredStockSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant