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Investments - Summary of Short-term and Long-term Investments (Detail) - USD ($) | Jun. 30, 2019 | Sep. 30, 2018
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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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