Marketable Securities and Fair Value Measurements - Company's Marketable Securities Measured at Fair Value (Detail) - USD ($)	Jun. 30, 2024	Sep. 30, 2023
Investment Holdings [Line Items]
Total	$ 87,805,000	$ 84,252,000
Exchange-Traded Funds [Member]
Investment Holdings [Line Items]
Total	3,557,000	3,327,000
Corporate Bonds [Member]
Investment Holdings [Line Items]
Total	31,452,000	33,160,000
Government Securities [Member]
Investment Holdings [Line Items]
Total	52,612,000	47,672,000
Cash and Money Funds [Member]
Investment Holdings [Line Items]
Total	184,000	93,000
Level 1 [Member]
Investment Holdings [Line Items]
Total	56,353,000	51,092,000
Level 1 [Member] | Exchange-Traded Funds [Member]
Investment Holdings [Line Items]
Total	3,557,000	3,327,000
Level 1 [Member] | Government Securities [Member]
Investment Holdings [Line Items]
Total	52,612,000	47,672,000
Level 1 [Member] | Cash and Money Funds [Member]
Investment Holdings [Line Items]
Total	184,000	93,000
Level 2 [Member]
Investment Holdings [Line Items]
Total	31,452,000	33,160,000
Level 2 [Member] | Corporate Bonds [Member]
Investment Holdings [Line Items]
Total	$ 31,452,000	$ 33,160,000