Components Of Equity - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Class of Stock [Line Items]
Date of declaration of dividends	May 02, 2012	May 04, 2011
Dividend declared per share	$ 0.28	$ 0.25
Date of dividend payment	Jun. 15, 2012	Jun. 15, 2011
Dividends payable to shareholders date of record	Jun. 01, 2012	Jun. 01, 2011