Income Taxes - Summary of Average Taxable Nature of Dividends (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common [Member]
Income Tax Contingency [Line Items]
Total dividends per share, common (usd per share)	$ 0.685	$ 0.68	$ 0.67
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	96.73%	63.07%	49.44%
Common [Member] | 15% Rate, Qualifying Dividend [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.22%	0.00%	0.05%
Common [Member] | 15% Rate Gain [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.00%	0.00%	0.00%
Common [Member] | Return of Capital [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	3.05%	36.93%	50.51%
Series C Cumulative Redeemable Preferred Shares [Member]
Income Tax Contingency [Line Items]
Total dividends per share, preferred (usd 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	99.78%	100.00%	99.90%
Series C Cumulative Redeemable Preferred Shares [Member] | 15% Rate, Qualifying Dividend [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.22%	0.00%	0.10%
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%	0.00%
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%