Schedule of Dividends Paid and Declared (Detail) (USD $)	3 Months Ended						12 Months Ended	0 Months Ended	6 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2011	Jul. 11, 2012 Dividend Declared	Jul. 11, 2012 Dividend Declared
Dividends Payable [Line Items]
Dividends paid per share	$ 0.17	$ 0.17	$ 0.14	$ 0.13	$ 0.13	$ 0.25	$ 0.65
Dividend declared per share								$ 0.19
Dividend paid and/or declared, per share									$ 0.53