Company's Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Sep. 30, 2012
Asset-backed and mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	$ 99,884	$ 120,326
Available-for-sale Securities, Gross Unrealized Gain	7,891	6,730
Available-for-sale Securities, Gross Unrealized Loss	(378)	(473)
Available-for-sale Securities, Fair Value	107,397	126,583
U.S. government and agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	35,179	58,350
Available-for-sale Securities, Gross Unrealized Gain	799	895
Available-for-sale Securities, Gross Unrealized Loss	(3)	(1)
Available-for-sale Securities, Fair Value	35,975	59,244
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	12,146	16,523
Available-for-sale Securities, Gross Unrealized Gain	153	170
Available-for-sale Securities, Gross Unrealized Loss	(27)	0
Available-for-sale Securities, Fair Value	12,272	16,693
Short-term Debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	147,209	195,199
Available-for-sale Securities, Gross Unrealized Gain	8,843	7,795
Available-for-sale Securities, Gross Unrealized Loss	(408)	(474)
Available-for-sale Securities, Fair Value	155,644	202,520
Long-term marketable equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	669	669
Available-for-sale Securities, Gross Unrealized Gain	846	1,541
Available-for-sale Securities, Gross Unrealized Loss	(1)	(1)
Available-for-sale Securities, Fair Value	$ 1,514	$ 2,209

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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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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