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Investments - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
Investments - Narrative (Details) - USD ($)	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Feb. 05, 2021	Sep. 30, 2020
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Other-than-temporary impairment charges recognized	$ 0	$ 0	$ 0	$ 0
Realized gains (losses) from sale of available-for-sale securities	0	$ 0	0	$ 0
Acquisition-related consideration, current	9,950,000		9,950,000			$ 753,000
Acquisition-related consideration, noncurrent	$ 5,330,000		$ 5,330,000
2026 Notes \| Convertible Debt
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Debt issued					$ 155,300,000
Debt interest rate					0.75%