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Stockholders' Equity - Additional Information (Detail) (USD $)
9 Months Ended 1 Months Ended 3 Months Ended
Sep. 30, 2012
Jun. 30, 2012
Stock Repurchase Plan
Sep. 30, 2012
Stock Repurchase Plan
Stockholders Equity [Line Items]      
Board of Directors authorized stock repurchase program   $ 250,000,000  
Stock repurchase remaining authorized amount     230,000,000
Number of shares that have been repurchased and retired during the period     757,650
Average price per share     $ 26.40
Value of shares that have been repurchased and retired during the period $ 20,013,000   $ 20,000,000
Stock repurchase program, period   2 years