Computations of Basic and Diluted Earnings Per Share (Parenthetical) (Detail) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share Disclosure [Line Items]
Shares of unvested restricted stock	1,406	1,274	1,076

This element represents nonvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid). Basic and dilutive earnings per share are generally disclosed for such shares using the two-class method.

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+ Details