Income Taxes - Summary of Average Taxable Nature of Dividends (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common [Member]
Income Tax Contingency [Line Items]
Total dividends per share, common (in dollars per share)	$ 0.68	$ 0.67	$ 0.6
Taxable percentage allocation on dividends	100.00%	100.00%	100.00%
Common [Member] | Ordinary Income [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	63.07%	49.44%	35.53%
Common [Member] | 15% Rate, Qualifying Dividend [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.00%	0.05%	4.11%
Common [Member] | 15% Rate Gain [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.00%	0.00%	2.09%
Common [Member] | Return of Capital [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	36.93%	50.51%	58.27%
Series C Cumulative Redeemable Preferred Shares [Member]
Income Tax Contingency [Line Items]
Total dividends per share, preferred (in dollars per share)	$ 3.25	$ 3.25	$ 3.25
Taxable percentage allocation on dividends	100.00%	100.00%	100.00%
Series C Cumulative Redeemable Preferred Shares [Member] | Ordinary Income [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	100.00%	99.90%	85.14%
Series C Cumulative Redeemable Preferred Shares [Member] | 15% Rate, Qualifying Dividend [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.00%	0.10%	9.85%
Series C Cumulative Redeemable Preferred Shares [Member] | 15% Rate Gain [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.00%	0.00%	5.01%
Series C Cumulative Redeemable Preferred Shares [Member] | Return of Capital [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.00%	0.00%	0.00%
Series D Cumulative Redeemable Preferred Shares [Member]
Income Tax Contingency [Line Items]
Total dividends per share, preferred (in dollars per share)	$ 0	$ 0	$ 1.043368
Taxable percentage allocation on dividends	0.00%	0.00%	100.00%
Series D Cumulative Redeemable Preferred Shares [Member] | Ordinary Income [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.00%	0.00%	85.14%
Series D Cumulative Redeemable Preferred Shares [Member] | 15% Rate, Qualifying Dividend [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.00%	0.00%	9.85%
Series D Cumulative Redeemable Preferred Shares [Member] | 15% Rate Gain [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.00%	0.00%	5.01%
Series D Cumulative Redeemable Preferred Shares [Member] | Return of Capital [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.00%	0.00%	0.00%