Income Tax Treatment of Distributions (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Treatment of Distributions and Dividends [Line Items]
Common stock dividends declared (per share)	$ 4.00	$ 3.73	$ 3.45
Common Stock
Income Tax Treatment of Distributions and Dividends [Line Items]
Ordinary income	62.40%	69.90%	62.10%
Return of capital	3.20%	3.80%	27.20%
Capital gains at 25%	2.20%	0.10%	0.70%
Capital gains at 20%	32.20%	26.20%	10.00%
Total	100.00%	100.00%	100.00%
Common stock dividends declared (per share)	$ 4.00	$ 3.73	$ 3.45
Series D Convertible Preferred Stock
Income Tax Treatment of Distributions and Dividends [Line Items]
Ordinary income	64.40%	72.70%	85.30%
Return of capital	0.00%	0.00%	0.00%
Capital gains at 25%	2.20%	0.10%	1.00%
Capital gains at 20%	33.40%	27.20%	13.70%
Total	100.00%	100.00%	100.00%
Common stock dividends declared (per share)	$ 1.3125	$ 1.75	$ 1.75
Series E Cumulative Redeemable Preferred Stock
Income Tax Treatment of Distributions and Dividends [Line Items]
Ordinary income			85.30%
Return of capital			0.00%
Capital gains at 25%			1.00%
Capital gains at 20%			13.70%
Total			100.00%
Common stock dividends declared (per share)			$ 0.4031