Fair Value Measurements - Fair Value Measurements for Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Mar. 31, 2022	Sep. 30, 2021
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Commercial Notes	$ 26,678
Marketable securities	122,575	$ 126,728
Held to Maturity, Fair Value	142,830	57,430
Long-term investments	195,726	196,643
Certificate of deposits	50,000	50,000
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	122,575	126,728
Certificate of deposits	50,000	50,000
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Commercial Notes	26,678
Held to Maturity, Fair Value	142,830	57,430
Long-term investments	$ 195,726	$ 196,643