Marketable Securities Summary of Marketable Securities Including Accrued Interest Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Sep. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 85,404	$ 145,391
Gross Unrealized Gains	84	221
Gross Unrealized Losses	(35)	(20)
Fair Value	85,453	145,592
U.S. Treasury securities and obligations of U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,786	41,202
Gross Unrealized Gains	9	15
Gross Unrealized Losses	(1)	(2)
Fair Value	22,794	41,215
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	37,581	64,102
Gross Unrealized Gains	26	138
Gross Unrealized Losses	(32)	(16)
Fair Value	37,575	64,224
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,171	1,310
Gross Unrealized Gains	39	42
Gross Unrealized Losses	0	(1)
Fair Value	1,210	1,351
Other debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	62	13
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	62	13
Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,755	34,777
Gross Unrealized Gains	10	25
Gross Unrealized Losses	(2)	(1)
Fair Value	19,763	34,801
Bank certificate of deposits
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,049	3,987
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	0
Fair Value	$ 4,049	$ 3,988

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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