Condensed Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Total Shareholders' Equity	Common Stock Class A Common Stock	Common Stock Class B-1 Common Stock	Common Stock Class B-2 Common Stock	Additional Paid In Capital	Retained Earnings	Cumulative Common Distributions	Noncontrolling Interest
Balance beginning at Sep. 30, 2020	$ 540,902	$ 295,919	$ 15	$ 1	$ 15	$ 106,622	$ 286,249	$ (96,983)	$ 244,983
Increase (Decrease) in Shareholders' Equity
Share awards, 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	299,598	15	1	15	107,634	295,146	(103,213)	248,519
Balance beginning at Sep. 30, 2020	540,902	295,919	15	1	15	106,622	286,249	(96,983)	244,983
Increase (Decrease) in Shareholders' Equity
Net income	31,233
Balance ending at Mar. 31, 2021	545,706	299,607	15	1	15	108,932	300,087	(109,443)	246,099
Balance beginning at Dec. 31, 2020	548,117	299,598	15	1	15	107,634	295,146	(103,213)	248,519
Increase (Decrease) in Shareholders' Equity
Share awards, 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	299,607	15	1	15	108,932	300,087	(109,443)	246,099
Balance beginning at Sep. 30, 2021	347,715	195,120	15	1	15	109,910	321,945	(236,766)	152,595
Increase (Decrease) in Shareholders' Equity
Share awards, net	613	613				613
Net income	18,292	8,042					8,042		10,250
Tax distributions to member	(1,979)								(1,979)
Common share distributions	(10,764)	(6,264)						(6,264)	(4,500)
Balance ending at Dec. 31, 2021	353,877	197,511	15	1	15	110,523	329,987	(243,030)	156,366
Balance beginning at Sep. 30, 2021	347,715	195,120	15	1	15	109,910	321,945	(236,766)	152,595
Increase (Decrease) in Shareholders' Equity
Net income	32,881
Balance ending at Mar. 31, 2022	354,569	198,783	16	1	15	111,667	336,379	(249,295)	155,786
Balance beginning at Dec. 31, 2021	353,877	197,511	$ 15	1	15	110,523	329,987	(243,030)	156,366
Increase (Decrease) in Shareholders' Equity
​Share awards, net (in shares)			1
Share awards, net	1,145	1,145				1,144
Net income	14,589	6,392					6,392		8,197
Tax distributions to member	(4,277)								(4,277)
Common share distributions	(10,765)	(6,265)						(6,265)	(4,500)
Balance ending at Mar. 31, 2022	$ 354,569	$ 198,783	$ 16	$ 1	$ 15	$ 111,667	$ 336,379	$ (249,295)	$ 155,786