Cash Equivalents and Investments - Company's Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Asset-backed and mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	$ 125,563	$ 99,884
Available-for-sale securities, Gross Unrealized Gain	6,390	7,891
Available-for-sale securities, Gross Unrealized Loss	(1,097)	(378)
Available-for-sale securities, Fair Value	130,856	107,397
Government and agencies securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	65,904	35,179
Available-for-sale securities, Gross Unrealized Gain	802	799
Available-for-sale securities, Gross Unrealized Loss	(6)	(3)
Available-for-sale securities, Fair Value	66,700	35,975
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	5,864	12,146
Available-for-sale securities, Gross Unrealized Gain	137	153
Available-for-sale securities, Gross Unrealized Loss		(27)
Available-for-sale securities, Fair Value	6,001	12,272
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	900
Available-for-sale securities, Gross Unrealized Gain
Available-for-sale securities, Gross Unrealized Loss
Available-for-sale securities, Fair Value	900
Short-term Debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	198,231	147,209
Available-for-sale securities, Gross Unrealized Gain	7,329	8,843
Available-for-sale securities, Gross Unrealized Loss	(1,103)	(408)
Available-for-sale securities, Fair Value	204,457	155,644
Long-term marketable equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale equity securities, Amortized Cost	669	669
Available-for-sale securities, Gross Unrealized Gain	1,020	846
Available-for-sale securities, Gross Unrealized Loss		(1)
Available-for-sale securities, Fair Value	$ 1,689	$ 1,514

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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