Marketable Securities Summary of Marketable Securities Including Accrued Interest Receivable (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Dec. 31, 2014	Sep. 30, 2013	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 141,183		$ 151,521
Gross Unrealized Gains	37	63
Gross Unrealized Losses	(284)	(242)
Fair Value	140,936us-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	29,054		26,052
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(45)	(39)
Fair Value	29,009		26,014
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	64,948		74,614
Gross Unrealized Gains	4	23
Gross Unrealized Losses	(198)	(174)
Fair Value	64,754		74,463
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	937		964
Gross Unrealized Gains	31	36
Gross Unrealized Losses	0	0
Fair Value	968		1,000
Other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,361		7,358
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(9)	(10)
Fair Value	7,352		7,348
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,800		15,888
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(31)	(16)
Fair Value	18,770		15,873
Bank certificate of deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	20,083		26,645
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(1)	(3)
Fair Value	$ 20,083		$ 26,644

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

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Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

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