Shareholders' Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended		12 Months Ended
	Dec. 31, 2010	Jul. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Jan. 28, 2005
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares issued			250,000,000
Preferred stock shares			15,000,000
Preferred stock issued	0		0	0
Preferred stock outstanding	0		0	0
Dividend declaration date			Dec. 10, 2004
Dividend payable date			Jan. 28, 2005
Dividend payable shareholders of record date			Jan. 28, 2005
Minimum percentage of ownership acquired exercise purchase right			15.00%
Rights redemption amount per right					0.0025
Authorized amount to repurchase shares of common stock	$ 25	$ 25	$ 25
Common stock shares repurchased			389,300	734,603
Common stock amount repurchased			$ 12.5	$ 25.0
Authorization expiry date			2012-12
Series A Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Preferred stock shares new issuance date			Dec. 10, 2004
Preferred stock shares new issuance			2,500,000
Series A Junior Participating Preferred Stock, par value			$ 0.10
Price of right per one hundredth of a share			240.00