Federal Income Taxes - Schedule of Characterized Distributions Paid per Common Share (Details) - $ / shares	3 Months Ended												12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Characterization Of Distributions [Line Items]
Amount of distributions paid per common share	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.72	$ 0.72	$ 0.72
Percentage of distributions paid per common share													100.00%	100.00%	100.00%
Ordinary Income [Member]
Characterization Of Distributions [Line Items]
Amount of distributions paid per common share													$ 0.09549	$ 0.00000	$ 0.01114
Percentage of distributions paid per common share													13.26%	0.00%	1.55%
Capital Gains [Member]
Characterization Of Distributions [Line Items]
Amount of distributions paid per common share													$ 0.01425	$ 0.00000	$ 0.00265
Percentage of distributions paid per common share													1.98%	0.00%	0.37%
Return Of Capital [Member]
Characterization Of Distributions [Line Items]
Amount of distributions paid per common share													$ 0.61026	$ 0.72000	$ 0.70621
Percentage of distributions paid per common share													84.76%	100.00%	98.08%