Income Taxes (Distributions Paid) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common Shares [Member]
Class of Stock [Line Items]
Ordinary Non-Qualified Income Per Share	$ 1.3794	$ 1.1715	$ 0.9108
Qualified Dividend per Share	0.0704	0.0213	0.0000
Capital Gain Per Share	0.0000	0.0000	0.0000
Return of Capital Per Share	0.0000	0.0000	0.0000
Distributions Paid Per Share on a Tax Basis	$ 1.4498	$ 1.1928	$ 0.9108
Percentage of Ordinary Non-Qualified Income	95.14%	98.21%	100.00%
Percentage of Qualified Dividend	4.86%	1.79%	0.00%
Percentage of Capital Gain	0.00%	0.00%	0.00%
Percentage of Return of Capital	0.00%	0.00%	0.00%
Percentage of Distributions Paid Per Share on a Tax Basis	100.00%	100.00%	100.00%
7.875% Series A
Class of Stock [Line Items]
Ordinary Non-Qualified Income Per Share	$ 0.2914	$ 1.9336	$ 2.3948
Qualified Dividend per Share	0.0149	0.0352	0.0000
Capital Gain Per Share	0.0000	0.0000	0.0000
Return of Capital Per Share	0.0000	0.0000	0.0000
Distributions Paid Per Share on a Tax Basis	$ 0.3063	$ 1.9688	$ 2.3948
Percentage of Ordinary Non-Qualified Income	95.14%	98.21%	100.00%
Percentage of Qualified Dividend	4.86%	1.79%	0.00%
Percentage of Capital Gain	0.00%	0.00%	0.00%
Percentage of Return of Capital	0.00%	0.00%	0.00%
Percentage of Distributions Paid Per Share on a Tax Basis	100.00%	100.00%	100.00%
8.00% Series B [Member]
Class of Stock [Line Items]
Ordinary Non-Qualified Income Per Share	$ 1.3109	$ 1.9643	$ 2.4328
Qualified Dividend per Share	0.0669	0.0357	0.0000
Capital Gain Per Share	0.0000	0.0000	0.0000
Return of Capital Per Share	0.0000	0.0000	0.0000
Distributions Paid Per Share on a Tax Basis	$ 1.3778	$ 2.0000	$ 2.4328
Percentage of Ordinary Non-Qualified Income	95.14%	98.21%	100.00%
Percentage of Qualified Dividend	4.86%	1.79%	0.00%
Percentage of Capital Gain	0.00%	0.00%	0.00%
Percentage of Return of Capital	0.00%	0.00%	0.00%
Percentage of Distributions Paid Per Share on a Tax Basis	100.00%	100.00%	100.00%
6.50% Series C [Member]
Class of Stock [Line Items]
Ordinary Non-Qualified Income Per Share	$ 1.5461	$ 1.5960	$ 1.9767
Qualified Dividend per Share	0.0789	0.0290	0.0000
Capital Gain Per Share	0.0000	0.0000	0.0000
Return of Capital Per Share	0.0000	0.0000	0.0000
Distributions Paid Per Share on a Tax Basis	$ 1.6250	$ 1.6250	$ 1.9767
Percentage of Ordinary Non-Qualified Income	95.14%	98.22%	100.00%
Percentage of Qualified Dividend	4.86%	1.78%	0.00%
Percentage of Capital Gain	0.00%	0.00%	0.00%
Percentage of Return of Capital	0.00%	0.00%	0.00%
Percentage of Distributions Paid Per Share on a Tax Basis	100.00%	100.00%	100.00%
6.375% Series D [Member]
Class of Stock [Line Items]
Ordinary Non-Qualified Income Per Share	$ 0.9099	$ 0.0000	$ 0.0000
Qualified Dividend per Share	0.0464	0.0000	0.0000
Capital Gain Per Share	0.0000	0.0000	0.0000
Return of Capital Per Share	0.0000	0.0000	0.0000
Distributions Paid Per Share on a Tax Basis	$ 0.9563	$ 0.0000	$ 0.0000
Percentage of Ordinary Non-Qualified Income	95.15%	0.00%	0.00%
Percentage of Qualified Dividend	4.85%	0.00%	0.00%
Percentage of Capital Gain	0.00%	0.00%	0.00%
Percentage of Return of Capital	0.00%	0.00%	0.00%
Percentage of Distributions Paid Per Share on a Tax Basis	100.00%	0.00%	0.00%