Common Stock Repurchases - Additional Information (Detail) (USD $) Share data in Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share Repurchases [Line Items]
Maximum amount authorized under stock repurchase program	$ 500,000,000	$ 750,000,000	$ 250,000,000
Value of shares remaining under stock repurchase program	478,600,000
Date the Company's board of directors authorized an additional stock repurchase program	2012
Shares repurchased during the year, shares	36.0	72.4	51.4
Shares repurchased during the year, value	$ 272,585,000	$ 498,786,000	$ 249,942,000