Marketable Securities and Fair Value Measurements - Company's Assets Measured at Fair Value (Detail) - USD ($)	Dec. 31, 2021	Sep. 30, 2021
Investment Holdings [Line Items]
Total	$ 95,682,000	$ 94,976,000
Equities [Member]
Investment Holdings [Line Items]
Total	19,646,000	14,734,000
Mutual Funds [Member]
Investment Holdings [Line Items]
Total	10,383,000	10,357,000
Exchange Traded Funds [Member]
Investment Holdings [Line Items]
Total	10,084,000	9,458,000
Corporate Bonds [Member]
Investment Holdings [Line Items]
Total	24,562,000	24,853,000
Government Securities [Member]
Investment Holdings [Line Items]
Total	26,999,000	30,999,000
Cash and Money Funds [Member]
Investment Holdings [Line Items]
Total	4,008,000	4,575,000
Level 1 [Member]
Investment Holdings [Line Items]
Total	71,120,000	70,123,000
Level 1 [Member] | Equities [Member]
Investment Holdings [Line Items]
Total	19,646,000	14,734,000
Level 1 [Member] | Mutual Funds [Member]
Investment Holdings [Line Items]
Total	10,383,000	10,357,000
Level 1 [Member] | Exchange Traded Funds [Member]
Investment Holdings [Line Items]
Total	10,084,000	9,458,000
Level 1 [Member] | Corporate Bonds [Member]
Investment Holdings [Line Items]
Total	0
Level 1 [Member] | Government Securities [Member]
Investment Holdings [Line Items]
Total	26,999,000	30,999,000
Level 1 [Member] | Cash and Money Funds [Member]
Investment Holdings [Line Items]
Total	4,008,000	4,575,000
Level 2 [Member]
Investment Holdings [Line Items]
Total	24,562,000	24,853,000
Level 2 [Member] | Equities [Member]
Investment Holdings [Line Items]
Total	0
Level 2 [Member] | Mutual Funds [Member]
Investment Holdings [Line Items]
Total	0
Level 2 [Member] | Exchange Traded Funds [Member]
Investment Holdings [Line Items]
Total	0
Level 2 [Member] | Corporate Bonds [Member]
Investment Holdings [Line Items]
Total	24,562,000	$ 24,853,000
Level 2 [Member] | Government Securities [Member]
Investment Holdings [Line Items]
Total	0
Level 2 [Member] | Cash and Money Funds [Member]
Investment Holdings [Line Items]
Total	0
Level 3 [Member]
Investment Holdings [Line Items]
Total	0
Level 3 [Member] | Equities [Member]
Investment Holdings [Line Items]
Total	0
Level 3 [Member] | Mutual Funds [Member]
Investment Holdings [Line Items]
Total	0
Level 3 [Member] | Exchange Traded Funds [Member]
Investment Holdings [Line Items]
Total	0
Level 3 [Member] | Corporate Bonds [Member]
Investment Holdings [Line Items]
Total	0
Level 3 [Member] | Government Securities [Member]
Investment Holdings [Line Items]
Total	0
Level 3 [Member] | Cash and Money Funds [Member]
Investment Holdings [Line Items]
Total	$ 0