Annual report pursuant to Section 13 and 15(d)

Dividends (Parenthetical) (Detail)

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Dividends (Parenthetical) (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended 12 Months Ended
Dec. 31, 2011
Dec. 31, 2012
Restricted Stock Units (RSUs)
Dec. 31, 2011
Restricted Stock Units (RSUs)
Dec. 31, 2010
Restricted Stock Units (RSUs)
Dividend Declared [Line Items]        
Dividends related to outstanding restricted stock units   $ 894 $ 684 $ 635
Effective Date of change in amount of quarterly dividend Nov. 02, 2010      
Revised quarterly dividend $ 0.21