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Stock Repurchase Plan - Additional Information (Detail) (USD $)
1 Months Ended 6 Months Ended 12 Months Ended 64 Months Ended
Feb. 29, 2012
Jun. 30, 2012
Dec. 31, 2011
Jun. 30, 2012
Maximum stock authorized to purchase under stock repurchase program $ 262,100,000   $ 210,000,000  
Increase in maximum stock authorized to purchase under stock repurchase program 52,100,000      
Repurchase of common stock, shares   1,125,792   9,207,972
Repurchase of common stock, value   44,064,000   231,100,000
Maximum remaining dollar value of shares authorized for purchase under the stock repurchase program   $ 31,000,000