Income Taxes (Taxability of Cash Distributions Paid on Common Shares) (Details) - Parent Company [Member] - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investments, Owned, Federal Income Tax Note
Ordinary income (dollars per share)	$ 3.66	$ 2.79	$ 3.28
Ordinary income (percentage per share)	99.30%	80.20%	100.00%
Return of capital (dollars per share)	$ 0.02	$ 0.31	$ 0
Return of capital (percentage per share)	0.60%	8.90%	0.00%
Un-recaptured Section 1250 gain dividends per share	$ 0.01	$ 0.38	$ 0.00
Un-recaptured Section 1250 gain dividends per share percentage	0.10%	10.90%	0.00%
Total (dollars per share)	$ 3.69	$ 3.48	$ 3.28
Total (percentage per share)	100.00%	100.00%	100.00%