Quarterly Financial Information (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019
Quarterly Financial Information Disclosure [Abstract]
Operating revenues	$ 9,780,289	$ 11,071,918	$ 22,437,731	$ 19,785,453	$ 9,851,869	$ 11,682,950	$ 25,274,959	$ 21,216,747	$ 63,075,391	$ 68,026,525
Operating income (loss)	(899,076)	1,335,663	6,999,616	5,081,979	490,702	1,637,057	6,203,483	3,264,222	12,518,182	11,595,464
Net income (loss)	$ (329,296)	$ 1,206,578	$ 5,680,316	$ 4,006,936	$ 455,605	$ 1,138,555	$ 4,670,090	$ 2,434,162	$ 10,564,534	$ 8,698,412
Earnings (loss) per share of common stock:
Basic (in usd per share)	$ (0.04)	$ 0.15	$ 0.70	$ 0.50	$ 0.06	$ 0.14	$ 0.58	$ 0.30	$ 1.30	$ 1.08
Diluted (in usd per share)	$ (0.04)	$ 0.15	$ 0.70	$ 0.49	$ 0.06	$ 0.14	$ 0.58	$ 0.30	$ 1.30	$ 1.08