Movements of Options Issued and Outstanding (Parenthetical) (Detail) (Stock Options, USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Market value of common stock	$ 4.39	$ 4.76	$ 11.24

Price of a single share of a number of saleable stocks of a company.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

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