Investments - Summary of Short-term, Long-term Investments and Marketable Securities (Detail) - USD ($)	Sep. 30, 2020	Sep. 30, 2019
Schedule Of Held To Maturity Securities And Marketable Securities [Line Items]
Held to Maturity, Amortized Cost	$ 224,376,634	$ 81,075,887
Held to Maturity, Gross Unrealized Gains	6,163,837	1,097,842
Held to Maturity, Gross Unrealized Losses	(79,471)
Held to Maturity, Fair Value	230,461,000	82,173,729
Marketable Securities, Amortized Cost	85,000,000
Marketable Securities, Realized Gains/(Losses)	94,734
Marketable Securities, Gross Unrealized Losses	(75,015)
Marketable Securities, Fair Value	85,019,719
Commercial Notes Due Within One Year
Schedule Of Held To Maturity Securities And Marketable Securities [Line Items]
Held to Maturity, Amortized Cost	86,889,751	36,899,894
Held to Maturity, Gross Unrealized Gains	1,589,873	222,584
Held to Maturity, Fair Value	88,479,624	37,122,478
Commercial Notes Due Within One Through Three Years
Schedule Of Held To Maturity Securities And Marketable Securities [Line Items]
Held to Maturity, Amortized Cost	137,486,883	44,175,993
Held to Maturity, Gross Unrealized Gains	4,573,964	875,258
Held to Maturity, Gross Unrealized Losses	(79,471)
Held to Maturity, Fair Value	141,981,376	$ 45,051,251
Marketable Securities
Schedule Of Held To Maturity Securities And Marketable Securities [Line Items]
Marketable Securities, Amortized Cost	85,000,000
Marketable Securities, Realized Gains/(Losses)	94,734
Marketable Securities, Gross Unrealized Losses	(75,015)
Marketable Securities, Fair Value	$ 85,019,719

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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