Marketable Securities and Fair Value Measurements - Company's Assets Measured at Fair Value (Detail) - USD ($)	Dec. 31, 2025	Sep. 30, 2025
Summary of Investment Holdings [Line Items]
Total	$ 111,003,000	$ 109,714,000
Level 1 [Member]
Summary of Investment Holdings [Line Items]
Total	80,212,000	78,127,000
Level 2 [Member]
Summary of Investment Holdings [Line Items]
Total	30,791,000	31,587,000
Equity Securities [Member]
Summary of Investment Holdings [Line Items]
Total	5,292,000	4,766,000
Equity Securities [Member] | Level 1 [Member]
Summary of Investment Holdings [Line Items]
Total	5,292,000	4,766,000
Mutual Funds [Member]
Summary of Investment Holdings [Line Items]
Total	3,087,000	2,098,000
Mutual Funds [Member] | Level 1 [Member]
Summary of Investment Holdings [Line Items]
Total	3,087,000	2,098,000
Exchange Traded Funds [Member]
Summary of Investment Holdings [Line Items]
Total	11,448,000	8,542,000
Exchange Traded Funds [Member] | Level 1 [Member]
Summary of Investment Holdings [Line Items]
Total	11,448,000	8,542,000
Corporate Bonds [Member]
Summary of Investment Holdings [Line Items]
Total	30,791,000	31,587,000
Corporate Bonds [Member] | Level 2 [Member]
Summary of Investment Holdings [Line Items]
Total	30,791,000	31,587,000
Government Securities [Member]
Summary of Investment Holdings [Line Items]
Total	59,972,000	62,462,000
Government Securities [Member] | Level 1 [Member]
Summary of Investment Holdings [Line Items]
Total	59,972,000	62,462,000
Cash and Money Funds [Member]
Summary of Investment Holdings [Line Items]
Total	413,000	259,000
Cash and Money Funds [Member] | Level 1 [Member]
Summary of Investment Holdings [Line Items]
Total	$ 413,000	$ 259,000