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Investments - Summary of Short-term and Long-term Investments (Detail) - USD ($) | Dec. 31, 2018 | Sep. 30, 2018
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Schedule Of Held To Maturity Securities [Line Items] |  |
Amortized Cost | $ 113,575,594 | $ 46,400,176
Gross Unrealized Gains | 228,825 |
Gross Unrealized Losses | (1,001,693) | (429,050)
Fair Value | 112,802,726 | 45,971,126
Commercial Notes Due Within One Year |  |
Schedule Of Held To Maturity Securities [Line Items] |  |
Amortized Cost | 53,980,307 | 46,400,176
Gross Unrealized Gains | 201,216 |
Gross Unrealized Losses | (799,900) | (429,050)
Fair Value | 53,381,623 | $ 45,971,126
Commercial Notes Due Within Two Years |  |
Schedule Of Held To Maturity Securities [Line Items] |  |
Amortized Cost | 59,595,287 |
Gross Unrealized Gains | 27,609 |
Gross Unrealized Losses | (201,793) |
Fair Value | $ 59,421,103 |

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