Marketable Securities Summary of Marketable Securities Including Accrued Interest Receivable (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 134,983	$ 151,521
Gross Unrealized Gains	71	63
Gross Unrealized Losses	(95)	(242)
Fair Value	134,959	151,342
U.S. Treasury securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	39,051	26,052
Gross Unrealized Gains	23	1
Gross Unrealized Losses	(10)	(39)
Fair Value	39,064	26,014
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	54,554	74,614
Gross Unrealized Gains	14	23
Gross Unrealized Losses	(55)	(174)
Fair Value	54,513	74,463
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	875	964
Gross Unrealized Gains	30	36
Gross Unrealized Losses	0	0
Fair Value	905	1,000
Other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,176	7,358
Gross Unrealized Gains	3	0
Gross Unrealized Losses	(1)	(10)
Fair Value	6,178	7,348
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,414	15,888
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(28)	(16)
Fair Value	19,386	15,873
Bank certificate of deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,913	26,645
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(1)	(3)
Fair Value	$ 14,913	$ 26,644