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Stockholders' Equity - Additional Information (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
1 Months Ended 9 Months Ended
Jun. 30, 2012
Sep. 30, 2012
Sep. 30, 2011
Stockholders Equity [Line Items]      
Sale of common stock, shares 6,500,000    
Sale of common stock, price per share $ 36.28    
Sale of common stock, proceeds $ 235,500 $ 235,499 $ 0