Marketable Securities - Summary of Marketable Securities Including Accrued Interest Receivable (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 133,263	$ 151,521
Gross Unrealized Gains	102	63
Gross Unrealized Losses	(57)	(242)
Fair Value	133,308	151,342
U.S. Treasury securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	30,343	26,052
Gross Unrealized Gains	39	1
Gross Unrealized Losses	0	(39)
Fair Value	30,382	26,014
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	54,725	74,614
Gross Unrealized Gains	13	23
Gross Unrealized Losses	(48)	(174)
Fair Value	54,690	74,463
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	857	964
Gross Unrealized Gains	$ 27	36
Gross Unrealized Losses		0
Fair Value	$ 884	1,000
Other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,056	7,358
Gross Unrealized Gains	$ 3	0
Gross Unrealized Losses		(10)
Fair Value	$ 5,059	7,348
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	30,258	15,888
Gross Unrealized Gains	18	1
Gross Unrealized Losses	(9)	(16)
Fair Value	30,267	15,873
Bank certificate of deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,024	26,645
Gross Unrealized Gains	$ 2	2
Gross Unrealized Losses		(3)
Fair Value	$ 12,026	$ 26,644