Marketable Securities - Company's Marketable Securities Measured at Fair Value (Detail) - USD ($)	Jun. 30, 2018	Sep. 30, 2017
Investment Holdings [Line Items]
Total	$ 87,900,000	$ 87,886,000
Equities [Member]
Investment Holdings [Line Items]
Total	12,288,000	11,338,000
Mutual Funds [Member]
Investment Holdings [Line Items]
Total	8,502,000	7,155,000
Exchange Traded Funds [Member]
Investment Holdings [Line Items]
Total	5,581,000	3,417,000
Corporate Bonds [Member]
Investment Holdings [Line Items]
Total	29,912,000	7,196,000
Government Securities [Member]
Investment Holdings [Line Items]
Total	28,944,000	54,542,000
Cash and Money Funds [Member]
Investment Holdings [Line Items]
Total	2,673,000	4,238,000
Level 1 [Member]
Investment Holdings [Line Items]
Total	57,988,000	80,690,000
Level 1 [Member] | Equities [Member]
Investment Holdings [Line Items]
Total	12,288,000	11,338,000
Level 1 [Member] | Mutual Funds [Member]
Investment Holdings [Line Items]
Total	8,502,000	7,155,000
Level 1 [Member] | Exchange Traded Funds [Member]
Investment Holdings [Line Items]
Total	5,581,000	3,417,000
Level 1 [Member] | Government Securities [Member]
Investment Holdings [Line Items]
Total	28,944,000	54,542,000
Level 1 [Member] | Cash and Money Funds [Member]
Investment Holdings [Line Items]
Total	2,673,000	4,238,000
Level 2 [Member]
Investment Holdings [Line Items]
Total	29,912,000	7,196,000
Level 2 [Member] | Corporate Bonds [Member]
Investment Holdings [Line Items]
Total	$ 29,912,000	$ 7,196,000