Investments - Summary of Short-term and Long-term Investments (Detail) - USD ($)	Mar. 31, 2019	Sep. 30, 2018
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	$ 124,096,728	$ 46,400,176
Gross Unrealized Gains	755,661
Gross Unrealized Losses	(162,798)	(429,050)
Fair Value	124,689,591	45,971,126
Commercial Notes Due Within One Year
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	56,560,674	46,400,176
Gross Unrealized Gains	52,189
Gross Unrealized Losses	(162,798)	(429,050)
Fair Value	56,450,065	$ 45,971,126
Commercial Notes Due Within Three Years
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	67,536,054
Gross Unrealized Gains	703,472
Fair Value	$ 68,239,526

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 45
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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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

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