Investments - Summary of Short-term, Long-term Investments and Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Sep. 30, 2022
Schedule Of Held To Maturity Securities And Marketable Securities [Line Items]
Short-term investments, Held to maturity, Adjusted Bases	$ 346,046	$ 268,391
Short-term investments, Held to maturity, Gross Unrealized Gains	0	0
Short-term investments, Held to maturity, Gross Unrealized Losses	(3,755)	(3,661)
Short-term investments, Held to maturity, Fair Value	342,291	264,730
Long-term investments, Held to maturity, Adjusted Basis	78,834	105,872
Long-term investments, Held to maturity, Gross Unrealized Gains	0	0
Long-term investments, Held to maturity, Gross Unrealized Losses	(1,709)	(5,569)
Long-term investments, Held to maturity, Fair Value	77,125	100,303
Debt securities
Schedule Of Held To Maturity Securities And Marketable Securities [Line Items]
Short-term investments, Held to maturity, Adjusted Bases	346,046	218,391
Short-term investments, Held to maturity, Gross Unrealized Gains	0	0
Short-term investments, Held to maturity, Gross Unrealized Losses	(3,755)	(3,661)
Short-term investments, Held to maturity, Fair Value	342,291	214,730
Long-term investments, Held to maturity, Adjusted Basis	78,834	105,872
Long-term investments, Held to maturity, Gross Unrealized Gains	0	0
Long-term investments, Held to maturity, Gross Unrealized Losses	(1,709)	(5,569)
Long-term investments, Held to maturity, Fair Value	77,125	100,303
Certificate of deposits
Schedule Of Held To Maturity Securities And Marketable Securities [Line Items]
Short-term investments, Held to maturity, Adjusted Bases	0	50,000
Short-term investments, Held to maturity, Gross Unrealized Gains	0	0
Short-term investments, Held to maturity, Gross Unrealized Losses	0	0
Short-term investments, Held to maturity, Fair Value	$ 0	$ 50,000