Other Data (Details 1) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Characterization of distributions on common stock
Ordinary income per share	$ 0.42	$ 0.78	$ 0.61
Return of capital per share	0.50	0.35	0.08
Unrecaptured section 1250 gain per share	0.28	0.07	0.51
Common stock distributions per share	$ 1.2	$ 1.2	$ 1.2
Ordinary income in percent of common stock distribution	34.50%	65.00%	51.00%
Return of capital in percent of common stock distribution	42.00%	29.50%	6.70%
Unrecaptured section 1250 gain in percent of common stock distribution	23.50%	5.50%	42.30%
Common stock distribution in percentage	100.00%	100.00%	100.00%