Investments - Summary of Short-term and Long-term Investments (Detail) - USD ($)	Dec. 31, 2019	Sep. 30, 2019
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	$ 67,298,439	$ 81,075,887
Gross Unrealized Gains	989,003	1,097,842
Fair Value	68,287,442	82,173,729
Commercial Notes Due Within One Year
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	40,969,341	36,899,894
Gross Unrealized Gains	362,500	222,584
Fair Value	41,331,841	37,122,478
Commercial Notes Due Within Two Years
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost	26,329,098
Gross Unrealized Gains	626,503
Fair Value	$ 26,955,601
Commercial Notes Due Within Three Year
Schedule Of Held To Maturity Securities [Line Items]
Amortized Cost		44,175,993
Gross Unrealized Gains		875,258
Fair Value		$ 45,051,251

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
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

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-Publisher FASB
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-Section 50
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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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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