Shareholders' Equity - Summary of Cash Distributions to Common Shareholders (Details) - USD ($)	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Cash distributions paid to common shareholders, Amount	$ 42,034,183	$ 35,522,127	$ 29,531,430
Cash distributions paid to common shareholders, Per Share	$ 0.64	$ 0.60	$ 0.60
December 31 [Member]
Cash distributions paid to common shareholders, Amount	$ 10,083,160	$ 8,598,414	$ 6,815,308
Cash distributions paid to common shareholders, Per Share	$ 0.16	$ 0.15	$ 0.15
March 31 [Member]
Cash distributions paid to common shareholders, Amount	$ 10,384,295	$ 8,765,446	$ 7,030,326
Cash distributions paid to common shareholders, Per Share	$ 0.16	$ 0.15	$ 0.15
June 30 [Member]
Cash distributions paid to common shareholders, Amount	$ 10,647,332	$ 8,952,767	$ 7,182,521
Cash distributions paid to common shareholders, Per Share	$ 0.16	$ 0.15	$ 0.15
September 30 [Member]
Cash distributions paid to common shareholders, Amount	$ 10,919,396	$ 9,205,500	$ 8,503,275
Cash distributions paid to common shareholders, Per Share	$ 0.16	$ 0.15	$ 0.15