Income Taxes Summary of the Average Taxable Nature of Dividends (Details) (USD $)

12 Months Ended

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Income Tax Contingency [Line Items]

Allocation of Dividend Payments

$ 0.349355

$ 0.12252

Common [Member]

Income Tax Contingency [Line Items]

Total dividends per share, common

$ 0.525

$ 0.46

$ 0.40

Taxable percentage allocation on dividends

100.00%

Common [Member] | Ordinary Income [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

95.68%

47.33%

99.11%

Common [Member] | Fifteen Percent Rate, Qualifying Dividend [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

0.99%

1.11%

0.89%

Common [Member] | Fifteen Percent Rate Gain [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

0.00%

Common [Member] | Twenty Five Percent Rate Gain [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

0.00%

Common [Member] | Return of Capital [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

3.33%

51.56%

0.00%

Series B Cumulative Redeemable Preferred Shares [Member]

Income Tax Contingency [Line Items]

Total dividends per share, preferred

$ 1.341667

$ 2.0125

Taxable percentage allocation on dividends

100.00%

Series B Cumulative Redeemable Preferred Shares [Member] | Ordinary Income [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

98.98%

97.70%

99.11%

Series B Cumulative Redeemable Preferred Shares [Member] | Fifteen Percent Rate, Qualifying Dividend [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

1.02%

2.30%

0.89%

Series B Cumulative Redeemable Preferred Shares [Member] | Fifteen Percent Rate Gain [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

0.00%

Series B Cumulative Redeemable Preferred Shares [Member] | Twenty Five Percent Rate Gain [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

0.00%

Series C

Income Tax Contingency [Line Items]

Total dividends per share, preferred

$ 3.25

Taxable percentage allocation on dividends

100.00%

Series C | Ordinary Income [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

98.98%

97.70%

99.11%

Series C | Fifteen Percent Rate, Qualifying Dividend [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

1.02%

2.30%

0.89%

Series C | Fifteen Percent Rate Gain [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

0.00%

Series C | Twenty Five Percent Rate Gain [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

0.00%

Series C | Return of Capital [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

0.00%

Series D Cumulative Redeemable Preferred Shares [Member]

Income Tax Contingency [Line Items]

Total dividends per share, preferred

$ 1.8875

$ 1.76498

^[1]

$ 2.01002

^[1]

Taxable percentage allocation on dividends

100.00%

Series D Cumulative Redeemable Preferred Shares [Member] | Ordinary Income [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

98.98%

97.70%

99.11%

Series D Cumulative Redeemable Preferred Shares [Member] | Fifteen Percent Rate, Qualifying Dividend [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

1.02%

2.30%

0.89%

Series D Cumulative Redeemable Preferred Shares [Member] | Fifteen Percent Rate Gain [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

0.00%

Series D Cumulative Redeemable Preferred Shares [Member] | Twenty Five Percent Rate Gain [Member]

Income Tax Contingency [Line Items]

Taxable percentage allocation on dividends

0.00%

[1]	Of the total dividend paid in January 2011, $0.12252 is allocated to 2010 and $0.349355 is allocated to 2011.