Components Of Equity And Comprehensive Income - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Class of Stock [Line Items]
Date of declaration of dividends	May 04, 2011	May 05, 2010
Dividend declared per share	$ 0.25	$ 0.20
Date of dividend payment	Jun. 15, 2011	Jun. 15, 2010
Dividends payable to shareholders date of record	Jun. 01, 2011	Jun. 01, 2010
Dividend Declared [Member]
Class of Stock [Line Items]
Date of declaration of dividends	Oct. 31, 2011
Dividend declared per share	$ 0.25
Date of dividend payment	Dec. 15, 2011
Dividends payable to shareholders date of record	Dec. 01, 2011