Cash Equivalents and Investments - Company's Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Long-term investments in 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	1,283	1,020
Available-for-sale securities, Gross Unrealized Loss
Available-for-sale securities, Fair Value	1,952	1,689
Asset-backed and mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	139,611	125,563
Available-for-sale securities, Gross Unrealized Gain	7,484	6,390
Available-for-sale securities, Gross Unrealized Loss	(829)	(1,097)
Available-for-sale securities, Fair Value	146,266	130,856
Government and agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	72,194	65,904
Available-for-sale securities, Gross Unrealized Gain	843	802
Available-for-sale securities, Gross Unrealized Loss	(2)	(6)
Available-for-sale securities, Fair Value	73,035	66,700
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	9,885	5,864
Available-for-sale securities, Gross Unrealized Gain	124	137
Available-for-sale securities, Gross Unrealized Loss	(3)
Available-for-sale securities, Fair Value	10,006	6,001
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	3,998	900
Available-for-sale securities, Gross Unrealized Gain
Available-for-sale securities, Gross Unrealized Loss
Available-for-sale securities, Fair Value	3,998	900
Total short-term debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Amortized Cost	225,688	198,231
Available-for-sale securities, Gross Unrealized Gain	8,451	7,329
Available-for-sale securities, Gross Unrealized Loss	(834)	(1,103)
Available-for-sale securities, Fair Value	$ 233,305	$ 204,457

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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