Selected Quarterly Financial Information (unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Selected Quarterly Financial Information (unaudited)
Revenues	$ 79,624,070	$ 68,559,782	$ 63,086,858	$ 62,950,738	$ 99,584,187	$ 88,479,024	$ 54,710,277	$ 73,165,324	$ 274,221,448	$ 315,938,812	$ 333,429,998
Operating income	37,476,803	22,550,972	19,115,310	13,255,888	46,290,595	41,875,535	5,413,760	22,519,802	92,398,973	116,099,692	161,068,831
Net income	$ 35,383,230	$ 16,580,885	$ 14,101,803	$ 5,869,100	$ 44,033,434	$ 35,825,264	$ 537,950	$ 12,168,005	$ 71,935,018	$ 92,564,653	$ 111,841,258
Earnings per common share - basic (in dollars per share)	$ 0.89	$ 0.42	$ 0.35	$ 0.14	$ 0.93	$ 0.71	$ 0.01	$ 0.24	$ 1.79	$ 1.86	$ 2.08
Earnings per common share - diluted (in dollars per share)	$ 0.88	$ 0.41	$ 0.35	$ 0.14	$ 0.93	$ 0.71	$ 0.01	$ 0.24	$ 1.78	$ 1.86	$ 2.07