Stockholder's Equity - Additional Information (Detail) (USD $)	1 Months Ended		9 Months Ended
	Aug. 31, 2012	Aug. 06, 2012	Sep. 30, 2012	Aug. 23, 2012	Jul. 25, 2011
Stockholders Equity [Line Items]
Repurchase of shares of common stock		5,000,000
Value of repurchase of shares of common stock		$ 185,400,000	$ 185,400,000
Company's credit facility			925,000,000		1,000,000,000
Shares sold upon exercise of options	846,469
Price of Option Shares sold				$ 40.00
Proceeds from sale of Option Shares	$ 32,722,000		$ 32,722,000