Components Of Equity - Additional Information (Detail) (USD $)	9 Months Ended		0 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Nov. 05, 2012 Subsequent Event
Class of Stock [Line Items]
Date of declaration of dividends	May 02, 2012	May 04, 2011	Nov. 05, 2012
Dividend declared per share	$ 0.28	$ 0.25	$ 0.28
Date of dividend payment	Jun. 15, 2012	Jun. 15, 2011	Dec. 17, 2012
Dividends payable to shareholders date of record	Jun. 01, 2012	Jun. 01, 2011	Dec. 03, 2012