Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Common shares Class A Common Stock	Common shares Class B-1 Common Stock	Common shares Class B-2 Common Stock	Additional Paid In Capital	Retained Earnings	Cumulative Common Distributions	Total Shareholders' Equity	Noncontrolling Interest
Balance beginning at Sep. 30, 2019	$ 529,035	$ 15	$ 1	$ 15	$ 103,360	$ 257,457	$ (72,194)	$ 288,654	$ 240,381
Increase (Decrease) in Shareholders' Equity
Share grants, net	634				634			634
Net income	21,624					9,449		9,449	12,175
Tax distributions to Member	(3,830)								(3,830)
Common share distributions	(10,695)						(6,195)	(6,195)	(4,500)
Balance ending at Dec. 31, 2019	536,768	15	1	15	103,994	266,906	(78,389)	292,542	244,226
Balance beginning at Sep. 30, 2019	529,035	15	1	15	103,360	257,457	(72,194)	288,654	240,381
Increase (Decrease) in Shareholders' Equity
Net income	36,545
Balance ending at Mar. 31, 2020	538,110	15	1	15	105,265	273,374	(84,583)	294,087	244,023
Balance beginning at Dec. 31, 2019	536,768	15	1	15	103,994	266,906	(78,389)	292,542	244,226
Increase (Decrease) in Shareholders' Equity
Share grants, net	1,271				1,271			1,271
Net income	14,921					6,468		6,468	8,453
Tax distributions to Member	(4,156)								(4,156)
Common share distributions	(10,694)						(6,194)	(6,194)	(4,500)
Balance ending at Mar. 31, 2020	538,110	15	1	15	105,265	273,374	(84,583)	294,087	244,023
Balance beginning at Sep. 30, 2020	540,902	15	1	15	106,622	286,249	(96,983)	295,919	244,983
Increase (Decrease) in Shareholders' Equity
Share grants, net	1,012				1,012			1,012
Net income	19,753					8,897		8,897	10,856
Tax distributions to Member	(2,820)								(2,820)
Common share distributions	(10,730)						(6,230)	(6,230)	(4,500)
Balance ending at Dec. 31, 2020	548,117	15	1	15	107,634	295,146	(103,213)	299,598	248,519
Balance beginning at Sep. 30, 2020	540,902	15	1	15	106,622	286,249	(96,983)	295,919	244,983
Increase (Decrease) in Shareholders' Equity
Net income	31,233
Balance ending at Mar. 31, 2021	545,706	15	1	15	108,932	300,087	(109,443)	299,607	246,099
Balance beginning at Dec. 31, 2020	548,117	15	1	15	107,634	295,146	(103,213)	299,598	248,519
Increase (Decrease) in Shareholders' Equity
Share grants, net	1,298				1,298			1,298
Net income	11,480					4,941		4,941	6,539
Tax distributions to Member	(4,459)								(4,459)
Common share distributions	(10,730)						(6,230)	(6,230)	(4,500)
Balance ending at Mar. 31, 2021	$ 545,706	$ 15	$ 1	$ 15	$ 108,932	$ 300,087	$ (109,443)	$ 299,607	$ 246,099