Income Taxes - Summary of Average Taxable Nature of Dividends (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Common [Member]
Income Tax Contingency [Line Items]
Total dividends per share, common (usd per share)	$ 0.71	$ 0.7	$ 0.685
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	87.89%	59.93%	96.73%
Common [Member] | 15% Rate, Qualifying Dividend [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.14%	0.15%	0.22%
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	11.97%	39.92%	3.05%
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	99.84%	99.75%	99.78%
Series C Cumulative Redeemable Preferred Shares [Member] | 15% Rate, Qualifying Dividend [Member]
Income Tax Contingency [Line Items]
Taxable percentage allocation on dividends	0.16%	0.25%	0.22%
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%