Marketable Securities - Company's Assets Measured at Fair Value (Detail) - USD ($)	Mar. 31, 2018	Sep. 30, 2017
Investment Holdings [Line Items]
Total	$ 88,004,000	$ 87,886,000
Equities [Member]
Investment Holdings [Line Items]
Total	13,835,000	11,338,000
Mutual Funds [Member]
Investment Holdings [Line Items]
Total	8,711,000	7,155,000
Exchange Traded Funds [Member]
Investment Holdings [Line Items]
Total	5,025,000	3,417,000
Corporate Bonds [Member]
Investment Holdings [Line Items]
Total	28,062,000	7,196,000
Government Securities [Member]
Investment Holdings [Line Items]
Total	27,976,000	54,542,000
Cash and Money Funds [Member]
Investment Holdings [Line Items]
Total	4,395,000	4,238,000
Level 1 [Member]
Investment Holdings [Line Items]
Total	59,942,000	80,690,000
Level 1 [Member] | Equities [Member]
Investment Holdings [Line Items]
Total	13,835,000	11,338,000
Level 1 [Member] | Mutual Funds [Member]
Investment Holdings [Line Items]
Total	8,711,000	7,155,000
Level 1 [Member] | Exchange Traded Funds [Member]
Investment Holdings [Line Items]
Total	5,025,000	3,417,000
Level 1 [Member] | Government Securities [Member]
Investment Holdings [Line Items]
Total	27,976,000	54,542,000
Level 1 [Member] | Cash and Money Funds [Member]
Investment Holdings [Line Items]
Total	4,395,000	4,238,000
Level 2 [Member]
Investment Holdings [Line Items]
Total	28,062,000	7,196,000
Level 2 [Member] | Corporate Bonds [Member]
Investment Holdings [Line Items]
Total	$ 28,062,000	$ 7,196,000