Fair Value Measurements - Fair Value Measurements for Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Mar. 31, 2020	Sep. 30, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 242,058,238	$ 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	256,650,727	221,804,128
Short-term investments	51,185,466	37,122,478
Long-term investments	190,872,772	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	256,650,727	221,804,128
Short-term investments	51,185,466	37,122,478
Long-term investments	$ 190,872,772	$ 45,051,251