Summary of Marketable Securities Including Accrued Interest Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Sep. 30, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 145,390		$ 147,177
Gross Unrealized Gains	120		102
Gross Unrealized Losses	(219)		(294)
Fair Value	145,291		146,985
U.S. Treasury securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	46,055		53,342
Gross Unrealized Gains	25		17
Gross Unrealized Losses	(5)		(21)
Fair Value	46,075		53,338
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	70,567		66,045
Gross Unrealized Gains	60		50
Gross Unrealized Losses	(152)		(203)
Fair Value	70,475		65,892
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,522	[1]	786	[1]
Gross Unrealized Gains	21	[1]	26	[1]
Gross Unrealized Losses	(52)	[1]	(3)	[1]
Fair Value	1,491	[1]	809	[1]
Other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	262		434
Fair Value	262		434
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,028		24,915
Gross Unrealized Gains	13		9
Gross Unrealized Losses	(10)		(67)
Fair Value	24,031		24,857
Bank certificate of deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,956		1,655
Gross Unrealized Gains	1
Fair Value	$ 2,957		$ 1,655

[1] Fair value amounts include approximately $0.7 million of investments in the Federal Home Loan Mortgage and Federal National Mortgage Association.