Tax Treatment of Distributions - Dividends Tax Treatment (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Treatment of Dividends Paid [Line Items]
Capital gains, federal statutory tax rate	20.00%
Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)	$ 1.955	$ 1.880	$ 1.760
Tax Treatment, Ordinary income [Member] | Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)	$ 1.474	$ 0.939	$ 1.474
Dividends paid per common share, percentage	75.40%	49.95%	83.73%
Tax Treatment, Qualified dividend [Member] | Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)	$ 0.002	$ 0.004	$ 0.003
Dividends paid per common share, percentage	0.12%	0.21%	0.19%
Tax Treatment, Return of capital [Member] | Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)	$ 0.162	$ 0.312	$ 0.275
Dividends paid per common share, percentage	8.30%	16.62%	15.64%
Tax Treatment, Capital gains [Member] | Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)	$ 0.275	$ 0.600	$ 0.008
Dividends paid per common share, percentage	14.05%	31.93%	0.44%
Tax Treatment, Unrecaptured section 1250 gains [Member] | Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)	$ 0.042	$ 0.025	$ 0
Dividends paid per common share, percentage	2.13%	1.29%	0.00%
Tax treatment [Member] | Common Stock [Member]
Income Tax Treatment of Dividends Paid [Line Items]
Dividends paid per common share (in dollars per share)	$ 1.955	$ 1.880	$ 1.760
Dividends paid per common share, percentage	100.00%	100.00%	100.00%