Income Taxes - Income Tax Purpose Distribution Paid to Preferred Shareholders are Classified as Ordinary Income (Detail) (USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Series J Preferred Stock [Member]
Income Tax [Line Items]
Ordinary Income			$ 0.3130	$ 1.4652
Long-term Capital Gains
Unrecaptured Section 1250 Gain				$ 0.2423
Return of Capital		$ 2.2657	$ 1.0402
Qualified Dividends			$ 0.0062	$ 0.1050
Preferred Distribution per Depository Share	$ 0.407812	$ 2.2657	$ 1.3594	$ 1.8125
Ordinary Income as a Percentage of Distribution		0.00%	23.02%	80.84%
Long-term Capital Gains as a Percentage of Distribution		0.00%	0.00%	0.00%
Unrecaptured Section 1250 Gain as a Percentage of Distribution		0.00%	0.00%	13.37%
Return of Capital as a Percentage of Distribution		100.00%	76.52%	0.00%
Qualified Dividends as a Percentage of Distribution		0.00%	0.46%	5.79%
Preferred Distribution, Percentage		100.00%	100.00%	100.00%
Series K Preferred Stock [Member]
Income Tax [Line Items]
Ordinary Income			$ 0.3130	$ 1.4652
Long-term Capital Gains
Unrecaptured Section 1250 Gain				$ 0.2423
Return of Capital		$ 2.2657	$ 1.0402
Qualified Dividends			$ 0.0062	$ 0.1050
Preferred Distribution per Depository Share		$ 2.2657	$ 1.3594	$ 1.8125
Ordinary Income as a Percentage of Distribution		0.00%	23.02%	80.84%
Long-term Capital Gains as a Percentage of Distribution		0.00%	0.00%	0.00%
Unrecaptured Section 1250 Gain as a Percentage of Distribution		0.00%	0.00%	13.37%
Return of Capital as a Percentage of Distribution		100.00%	76.52%	0.00%
Qualified Dividends as a Percentage of Distribution		0.00%	0.46%	5.79%
Preferred Distribution, Percentage		100.00%	100.00%	100.00%
Depositary Shares [Member] | Series J Preferred Stock [Member]
Income Tax [Line Items]
Ordinary Income
Long-term Capital Gains
Unrecaptured Section 1250 Gain
Return of Capital		$ 2.2203
Qualified Dividends
Preferred Distribution per Depository Share		$ 2.2203
Ordinary Income as a Percentage of Distribution
Long-term Capital Gains as a Percentage of Distribution		0.00%
Unrecaptured Section 1250 Gain as a Percentage of Distribution
Return of Capital as a Percentage of Distribution		100.00%
Qualified Dividends as a Percentage of Distribution
Preferred Distribution, Percentage		100.00%