Fair Value Measurements - Fair Value Measurements for Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Sep. 30, 2020	Sep. 30, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments (held to maturity)	$ 230,461,000	$ 82,173,729
Contingent Consideration	0	0
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	143,582,667	221,804,128
Marketable securities	85,019,719
Short-term investments (held to maturity)	88,479,624	37,122,478
Long-term investments (held to maturity)	141,981,376	45,051,251
Fair Value, Measurements, Recurring | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	143,582,667	221,804,128
Marketable securities	85,019,719
Fair Value, Measurements, Recurring | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments (held to maturity)	88,479,624	37,122,478
Long-term investments (held to maturity)	$ 141,981,376	$ 45,051,251