Marketable Securities Summary of Marketable Securities Including Accrued Interest Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 132,842	$ 151,521
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	1,140	63
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	54	242
Fair Value	133,928us-gaap_AvailableForSaleSecurities	151,342us-gaap_AvailableForSaleSecurities
U.S. Treasury securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	27,402	26,052
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	17	1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	2	39
Fair Value	27,417	26,014
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	61,377	74,614
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	26	23
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	38	174
Fair Value	61,365	74,463
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	911	964
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	30	36
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	0
Fair Value	941	1,000
Other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,270	7,358
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	2	0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	10
Fair Value	6,272	7,348
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,936	15,888
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	2	1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	14	16
Fair Value	19,924	15,873
Bank certificate of deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	16,946	26,645
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	1,063	2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	3
Fair Value	$ 18,009	$ 26,644

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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