Schedule of Restricted Stock Units Weighted Average Contractual Terms (Detail) (Restricted Stock Units)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Outstanding	1 year 4 days	1 year 15 days	1 year 1 month 17 days
Expected to vest	1 year	1 year 11 days	1 year 1 month 13 days

Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (e)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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