Income Taxes - Taxability of Cash Distributions Paid on Common Shares (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Ordinary income	$ 2.55	$ 2.67	$ 2.97
Capital gains	0.05	0.05	0.03
Return of capital	0.88		0.15
Total	$ 3.48	$ 2.72	$ 3.15