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Investments - Summary of Short-term and Long-term Investments (Detail) - USD ($)	Mar. 31, 2020	Sep. 30, 2019
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	$ 241,577,133	$ 81,075,887
Gross Unrealized Gains	2,000,006	1,097,842
Gross Unrealized Losses	(1,518,901)
Fair Value	242,058,238	82,173,729
Commercial Notes Due Within One Year
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	50,959,058	36,899,894
Gross Unrealized Gains	264,194	222,584
Gross Unrealized Losses	(37,786)
Fair Value	51,185,466	37,122,478
Commercial Notes Due Within One Through Three Years
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	190,618,075	44,175,993
Gross Unrealized Gains	1,735,812	875,258
Gross Unrealized Losses	(1,481,115)
Fair Value	$ 190,872,772	$ 45,051,251

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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