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Investments - Summary of Short-term and Long-term Investments (Detail) - USD ($)	Jun. 30, 2019	Sep. 30, 2018
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	$ 106,122,714	$ 46,400,176
Gross Unrealized Gains	1,145,937
Gross Unrealized Losses	(84,678)	(429,050)
Fair Value	107,183,973	45,971,126
Commercial Notes Due Within One Year
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	48,567,215	46,400,176
Gross Unrealized Gains	155,327
Gross Unrealized Losses	(84,678)	(429,050)
Fair Value	48,637,864	$ 45,971,126
Commercial Notes Due Within Three Years
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	57,555,499
Gross Unrealized Gains	990,610
Fair Value	$ 58,546,109

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

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