Amounts Charged to Expense for Stock-based Compensation (Parenthetical) (Detail) (Restricted stock units, USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reversal of RSU expense	$ 6.2

Reversal of share-based payment expense excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) related to performance based awards that are not expected to vest.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration