Tax Components of Common and Preferred Dividends Declared (Detail)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Dividends Payable [Line Items]
Ordinary income	34.00%	74.00%	69.00%
15% capital gain	47.00%	11.00%	21.00%
Unrecaptured section 1250 gain	19.00%	15.00%	10.00%