Condensed Balance Sheets (Parenthetical) (Detail) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Class A Ordinary Shares
Condensed Balance Sheet Statements, Captions [Line Items]
Ordinary shares, par value (in dollars per share)	$ 0.00001
Ordinary shares, shares authorized (in shares)	1,200,000,000	1,200,000,000
Ordinary shares, shares issued (in shares)	496,636,128	505,207,968
Ordinary shares, shares outstanding (in shares)	496,636,128	505,207,968
Class A Ordinary Shares \| Parent Company
Condensed Balance Sheet Statements, Captions [Line Items]
Ordinary shares, par value (in dollars per share)	$ 0.00001
Ordinary shares, shares authorized (in shares)	1,200,000,000	1,200,000,000
Ordinary shares, shares issued (in shares)	496,636,128	505,207,968
Ordinary shares, shares outstanding (in shares)	496,636,128	505,207,968
Class B Ordinary Shares
Condensed Balance Sheet Statements, Captions [Line Items]
Ordinary shares, par value (in dollars per share)	$ 0.00001
Ordinary shares, shares authorized (in shares)	300,000,000	300,000,000
Ordinary shares, shares issued (in shares)	174,649,638	174,649,638
Ordinary shares, shares outstanding (in shares)	174,649,638	174,649,638
Class B Ordinary Shares \| Parent Company
Condensed Balance Sheet Statements, Captions [Line Items]
Ordinary shares, par value (in dollars per share)	$ 0.00001
Ordinary shares, shares authorized (in shares)	300,000,000	300,000,000
Ordinary shares, shares issued (in shares)	174,649,638	174,649,638
Ordinary shares, shares outstanding (in shares)	174,649,638	174,649,638

Face amount or stated value per share of common stock.

Name:	us-gaap_CommonStockParOrStatedValuePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

+ References

+ Details

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

- Definition

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

+ References

+ Details

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

- Definition

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

+ References

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(29))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_CondensedBalanceSheetStatementsCaptionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConsolidatedEntitiesAxis=us-gaap_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: