Fair Value Measurements - Fair Value Measurements for Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2019	Sep. 30, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 68,287,442	$ 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	461,032,249	221,804,128
Short-term investments	41,331,841	37,122,478
Long-term investments	26,955,601	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	461,032,249	221,804,128
Short-term investments	41,331,841	37,122,478
Long-term investments	$ 26,955,601	$ 45,051,251