Fair Value Measurements - Fair Value Measurements for Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Sep. 30, 2021	Sep. 30, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments (held to maturity)	$ 304,073,000	$ 230,462,000
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	184,434,000	143,583,000
Marketable securities	126,728,000	85,020,000
Short-term investments (held to maturity)	57,430,000	88,480,000
Long-term investments (held to maturity)	246,643,000	141,982,000
Fair Value, Measurements, Recurring | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents	184,434,000	143,583,000
Marketable securities	126,728,000	85,020,000
Fair Value, Measurements, Recurring | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments (held to maturity)	57,430,000	88,480,000
Long-term investments (held to maturity)	$ 246,643,000	$ 141,982,000