Income Taxes - Distributions (Details) - $ / shares					1 Months Ended	12 Months Ended
	Dec. 16, 2019	Dec. 14, 2018	Dec. 15, 2017	Dec. 15, 2016	Dec. 14, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Common Shares
Real Estate Investment Trust Distributions [Line Items]
Ordinary non-qualified income (in usd per share)						$ 0.5609	$ 1.2040	$ 1.3611
Ordinary non-qualified income, percent						30.03%	77.57%	95.41%
Qualified dividend (in usd per share)						$ 0.0069	$ 0.3482	$ 0.0256
Qualified dividend, percent						0.37%	22.43%	1.79%
Capital gain (in usd per share)						$ 1.3000	$ 0	$ 0
Capital gain, percent						69.60%	0.00%	0.00%
Return of capital (in usd per share)						$ 0	$ 0	$ 0.0399
Return of capital, percent						0.00%	0.00%	2.80%
Total (in usd per share)						$ 1.8678	$ 1.5522	$ 1.4266
Total, percent						100.00%	100.00%	100.00%
Distributions declared, treated as distributions for taxes in next year (in usd per share)	$ 0.3800		$ 0.3800	$ 0.2866	$ 0.3478
Series C Cumulative Redeemable Preferred Shares
Real Estate Investment Trust Distributions [Line Items]
Ordinary non-qualified income (in usd per share)						$ 0.6100	$ 1.2605	$ 1.1969
Ordinary non-qualified income, percent						30.03%	77.57%	98.20%
Qualified dividend (in usd per share)						$ 0.0075	$ 0.3645	$ 0.0219
Qualified dividend, percent						0.37%	22.43%	1.80%
Capital gain (in usd per share)						$ 1.4138	$ 0	$ 0
Capital gain, percent						69.60%	0.00%	0.00%
Return of capital (in usd per share)						$ 0	$ 0	$ 0
Return of capital, percent						0.00%	0.00%	0.00%
Total (in usd per share)						$ 2.0313	$ 1.6250	$ 1.2188
Total, percent						100.00%	100.00%	100.00%
Distributions declared, treated as distributions for taxes in next year (in usd per share)		$ 0.4063
Series D Cumulative Redeemable Preferred Shares
Real Estate Investment Trust Distributions [Line Items]
Ordinary non-qualified income (in usd per share)						$ 0.5982	$ 1.2363	$ 1.1739
Ordinary non-qualified income, percent						30.03%	77.57%	98.21%
Qualified dividend (in usd per share)						$ 0.0074	$ 0.3575	$ 0.0214
Qualified dividend, percent						0.37%	22.43%	1.79%
Capital gain (in usd per share)						$ 1.3866	$ 0	$ 0
Capital gain, percent						69.60%	0.00%	0.00%
Return of capital (in usd per share)						$ 0	$ 0	$ 0
Return of capital, percent						0.00%	0.00%	0.00%
Total (in usd per share)						$ 1.9922	$ 1.5938	$ 1.1953
Total, percent						100.00%	100.00%	100.00%
Distributions declared, treated as distributions for taxes in next year (in usd per share)		0.3984
Series E Cumulative Redeemable Preferred Shares
Real Estate Investment Trust Distributions [Line Items]
Ordinary non-qualified income (in usd per share)						$ 0.5982	$ 0	$ 0
Ordinary non-qualified income, percent						30.03%	0.00%	0.00%
Qualified dividend (in usd per share)						$ 0.0074	$ 0	$ 0
Qualified dividend, percent						0.37%	0.00%	0.00%
Capital gain (in usd per share)						$ 1.3866	$ 0	$ 0
Capital gain, percent						69.60%	0.00%	0.00%
Return of capital (in usd per share)						$ 0	$ 0	$ 0
Return of capital, percent						0.00%	0.00%	0.00%
Total (in usd per share)						$ 1.9922	$ 0	$ 0
Total, percent						100.00%	0.00%	0.00%
Distributions declared, treated as distributions for taxes in next year (in usd per share)		0.3984
Series F Cumulative Redeemable Preferred Shares
Real Estate Investment Trust Distributions [Line Items]
Ordinary non-qualified income (in usd per share)						$ 0.5912	$ 0	$ 0
Ordinary non-qualified income, percent						30.03%	0.00%	0.00%
Qualified dividend (in usd per share)						$ 0.0073	$ 0	$ 0
Qualified dividend, percent						0.37%	0.00%	0.00%
Capital gain (in usd per share)						$ 1.3703	$ 0	$ 0
Capital gain, percent						69.60%	0.00%	0.00%
Return of capital (in usd per share)						$ 0	$ 0	$ 0
Return of capital, percent						0.00%	0.00%	0.00%
Total (in usd per share)						$ 1.9688	$ 0	$ 0
Total, percent						100.00%	0.00%	0.00%
Distributions declared, treated as distributions for taxes in next year (in usd per share)		$ 0.3938