Distributions - Tax Characteristics of Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Distributions [Abstract]
Common Share Distributions Payments of Ordinary Dividends	$ 0.38	$ 0	$ 0.36
Common Share Distributions Capital Gain	0.26	0.62	0.14
Common Share Distributions Non-taxable Distributions	0	0	0.10
Common Stock, Dividends, Per Share, Paid	$ 0.64	$ 0.62	$ 0.60
Percentage Of Distributions classified as ordinary income	60.00%	0.00%	59.10%
Percentage Of Distributions classified as capital gain	40.00%	100.00%	23.50%
Percentage Of Distributions classified as non-taxable distribution	0.00%	0.00%	17.40%
Dividends, Preferred Stock	$ 2,032	$ 6,900	$ 6,900
Percentage Of Preferred Distributions classified as ordinary income	60.00%	0.00%	71.60%
Percentage Of Preferred Distributions classified as capital gain	40.00%	100.00%	28.40%
Percentage Of Preferred Distributions classified as non-taxable distribution	0.00%	0.00%	0.00%