Income Taxes - Tax treatment of distributions to shareholders (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Ordinary income	$ 0.6625	$ 0	$ 0.8316
Long-term capital gain	1.2075	1.8200	0
Return of capital	0	0	0.9084
Total per common share outstanding	1.8700	1.8200	1.7400
Unrecaptured Section 1250 gains	$ 0.3827	$ 0.4008	$ 0