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Shareholders' Equity - Additional Information (Detail) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2011
Jun. 30, 2010
Jun. 30, 2011
Jun. 30, 2010
Stockholders Equity Note [Line Items]        
Repurchase and retirement of common stock     $ 32,856,000  
Repurchase and retirement of common stock, shares     419,000  
Repurchase of common stock, shares authorized to repurchase 2,700,000   2,700,000  
Cash dividend paid $ 0.45      
Cash dividend paid, Payment date May 16, 2011
Cash dividend paid, record date May 02, 2011
Cash dividend declared $ 0.45   $ 0.45  
Cash dividend declared, date Jul. 20, 2011
Cash dividends declared, payable date Aug. 15, 2011
Cash dividends declared, record date Aug. 01, 2011
Common stock excluded from calculation of diluted earnings per share 30,000 291,000 250,000 2,701,000