Tax Treatment of Distributions Tax Treatment of Distributions (Details 1) (USD $)	12 Months Ended			0 Months Ended	12 Months Ended			0 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended
	Dec. 31, 2012 Common Stock [Member]	Dec. 31, 2011 Common Stock [Member]	Dec. 31, 2010 Common Stock [Member]	Apr. 16, 2012 Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2010 Series E Cumulative Redeemable Preferred Stock [Member]	Apr. 16, 2012 Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2010 Series F Cumulative Redeemable Preferred Stock [Member]	Mar. 31, 2012 Series G Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series G Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series G Cumulative Redeemable Preferred Stock [Member]	Aug. 31, 2012 Series H Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series H Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series H Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Tax Treatment, Ordinary Income [Member] Common Stock [Member]	Dec. 31, 2011 Tax Treatment, Ordinary Income [Member] Common Stock [Member]	Dec. 31, 2010 Tax Treatment, Ordinary Income [Member] Common Stock [Member]	Dec. 31, 2012 Tax Treatment, Ordinary Income [Member] Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Tax Treatment, Ordinary Income [Member] Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2010 Tax Treatment, Ordinary Income [Member] Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Tax Treatment, Ordinary Income [Member] Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Tax Treatment, Ordinary Income [Member] Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2010 Tax Treatment, Ordinary Income [Member] Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Tax Treatment, Ordinary Income [Member] Series G Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Tax Treatment, Ordinary Income [Member] Series H Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Tax Treatment, Return of Capital [Member] Common Stock [Member]	Dec. 31, 2011 Tax Treatment, Return of Capital [Member] Common Stock [Member]	Dec. 31, 2010 Tax Treatment, Return of Capital [Member] Common Stock [Member]	Dec. 31, 2012 Tax Treatment, Capital Gains [Member] Common Stock [Member]		Dec. 31, 2011 Tax Treatment, Capital Gains [Member] Common Stock [Member]		Dec. 31, 2010 Tax Treatment, Capital Gains [Member] Common Stock [Member]		Dec. 31, 2012 Tax Treatment, Capital Gains [Member] Series E Cumulative Redeemable Preferred Stock [Member]		Dec. 31, 2011 Tax Treatment, Capital Gains [Member] Series E Cumulative Redeemable Preferred Stock [Member]		Dec. 31, 2010 Tax Treatment, Capital Gains [Member] Series E Cumulative Redeemable Preferred Stock [Member]		Dec. 31, 2012 Tax Treatment, Capital Gains [Member] Series F Cumulative Redeemable Preferred Stock [Member]		Dec. 31, 2011 Tax Treatment, Capital Gains [Member] Series F Cumulative Redeemable Preferred Stock [Member]		Dec. 31, 2010 Tax Treatment, Capital Gains [Member] Series F Cumulative Redeemable Preferred Stock [Member]		Dec. 31, 2012 Tax Treatment, Capital Gains [Member] Series G Cumulative Redeemable Preferred Stock [Member]		Dec. 31, 2012 Tax Treatment, Capital Gains [Member] Series H Cumulative Redeemable Preferred Stock [Member]		Dec. 31, 2012 Tax Treatment, Unrecaptured Section 1250 Gains [Member] Common Stock [Member]	Dec. 31, 2011 Tax Treatment, Unrecaptured Section 1250 Gains [Member] Common Stock [Member]	Dec. 31, 2010 Tax Treatment, Unrecaptured Section 1250 Gains [Member] Common Stock [Member]	Dec. 31, 2012 Tax Treatment, Unrecaptured Section 1250 Gains [Member] Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Tax Treatment, Unrecaptured Section 1250 Gains [Member] Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2010 Tax Treatment, Unrecaptured Section 1250 Gains [Member] Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Tax Treatment, Unrecaptured Section 1250 Gains [Member] Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Tax Treatment, Unrecaptured Section 1250 Gains [Member] Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2010 Tax Treatment, Unrecaptured Section 1250 Gains [Member] Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Tax Treatment, Unrecaptured Section 1250 Gains [Member] Series G Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Tax Treatment, Unrecaptured Section 1250 Gains [Member] Series H Cumulative Redeemable Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, dividend rate				7.80%		7.80%		7.50%		7.50%		6.875%	6.875%		6.375%	6.375%
Dividends paid per common share	$ 1.400	$ 1.400	$ 1.400															$ 0.577	$ 0.230	$ 0.000									$ 0.823	$ 1.170	$ 1.400	$ 0.000	[1]	$ 0.000	[1]	$ 0.000	[1]																	$ 0.000	$ 0.000	$ 0.000
Common Stock, Dividends, Per Share, Cash Paid, Percentage	100.00%	100.00%	100.00%															41.21%	16.43%	0.00%									58.79%	83.57%	100.00%	0.00%	[1]	0.00%	[1]	0.00%	[1]																	0.00%	0.00%	0.00%
Preferred Stock, Dividends, Per Share, Cash Paid					$ 0.818	$ 1.950	$ 1.950		$ 0.786	$ 1.875	$ 1.875		$ 1.089			$ 0.398					$ 0.818	$ 1.950	$ 1.950	$ 0.786	$ 1.875	$ 1.875	$ 1.089	$ 0.398										$ 0.000	[1]	$ 0.000	[1]	$ 0.000	[1]	$ 0.000	[1]	$ 0.000	[1]	$ 0.000	[1]	$ 0.000	[1]	$ 0.000	[1]				$ 0.000	$ 0.000	$ 0.000	$ 0.000	$ 0.000	$ 0.000	$ 0.000	$ 0.000
Preferred Stock, Dividends, Per Share, Cash Paid, Percentage					100.00%	100.00%	100.00%		100.00%	100.00%	100.00%		100.00%			100.00%					100.00%	100.00%	100.00%	100.00%	100.00%	100.00%	100.00%	100.00%										0.00%	[1]	0.00%	[1]	0.00%	[1]	0.00%	[1]	0.00%	[1]	0.00%	[1]	0.00%	[1]	0.00%	[1]				0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%	0.00%
Capital Gains, Percent	15.00%								15.00%							15.00%

[1] Capital gains are comprised entirely of 15% rate gains.