Marketable Securities - Company's Assets Measured at Fair Value (Detail) (USD $)	Mar. 31, 2015	Sep. 30, 2014
Investment Holdings [Line Items]
Total	$ 87,400,000	$ 87,112,000
Equities [Member]
Investment Holdings [Line Items]
Total	19,087,000	17,102,000
Mutual Funds [Member]
Investment Holdings [Line Items]
Total	12,406,000	19,088,000
Exchange-Traded Funds [Member]
Investment Holdings [Line Items]
Total	4,053,000	1,764,000
Government Securities [Member]
Investment Holdings [Line Items]
Total	43,899,000	43,999,000
Cash and Money Funds [Member]
Investment Holdings [Line Items]
Total	7,955,000	5,159,000
Level 1 [Member]
Investment Holdings [Line Items]
Total	87,400,000	87,112,000
Level 1 [Member] | Equities [Member]
Investment Holdings [Line Items]
Total	19,087,000	17,102,000
Level 1 [Member] | Mutual Funds [Member]
Investment Holdings [Line Items]
Total	12,406,000	19,088,000
Level 1 [Member] | Exchange-Traded Funds [Member]
Investment Holdings [Line Items]
Total	4,053,000	1,764,000
Level 1 [Member] | Government Securities [Member]
Investment Holdings [Line Items]
Total	43,899,000	43,999,000
Level 1 [Member] | Cash and Money Funds [Member]
Investment Holdings [Line Items]
Total	$ 7,955,000	$ 5,159,000