Investments - Summary of Short-term and Long-term Investments (Detail) - USD ($)	Jun. 30, 2018	Sep. 30, 2017
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	$ 50,157,366	$ 40,769,539
Gross Unrealized Losses	(335,334)	(334,755)
Fair Value	49,822,032	40,434,784
Commercial Notes Due Within One Year
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	32,484,708	40,769,539
Gross Unrealized Losses	(237,007)	(334,755)
Fair Value	32,247,701	$ 40,434,784
Commercial Notes Due After One year Through Two Years
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	17,672,658
Gross Unrealized Losses	(98,327)
Fair Value	$ 17,574,331

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 45
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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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-Name Accounting Standards Codification
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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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